# Knuth shuffle

The   Knuth shuffle   (a.k.a. the Fisher-Yates shuffle)   is an algorithm for randomly shuffling the elements of an array.

Implement the Knuth shuffle for an integer array (or, if possible, an array of any type).

Specification

Given an array items with indices ranging from 0 to last, the algorithm can be defined as follows (pseudo-code):

       for i from last downto 1 do:
let j = random integer in range 0 $\leq$ j $\leq$ i
swap items[i] with items[j]

Notes
•   It modifies the input array in-place.
•   If that is unreasonable in your programming language, you may amend the algorithm to return the shuffled items as a new array instead.
•   The algorithm can also be amended to iterate from left to right, if that is more convenient.

Test cases
Input array Possible output arrays
[] []
 
[10, 20] [10, 20]
[20, 10]
[10, 20, 30] [10, 20, 30]
[10, 30, 20]
[20, 10, 30]
[20, 30, 10]
[30, 10, 20]
[30, 20, 10]

(These are listed here just for your convenience; no need to demonstrate them on the page.)

## 11l

Translation of: Python
F knuth_shuffle(&x)
L(i) (x.len - 1 .< 0).step(-1)
V j = random:(0..i)
swap(&x[i], &x[j])

V x = Array(0..9)
knuth_shuffle(&x)
print(‘shuffled: ’x)
Output:
shuffled: [0, 5, 7, 1, 3, 8, 4, 6, 9, 2]


## 360 Assembly

Translation of: BBC BASIC
*        Knuth shuffle             02/11/2015
KNUTHSH  CSECT
USING  KNUTHSH,R15
LA     R6,1               i=1
LOOPI1   C      R6,=A(CARDS)       do i=1 to cards
BH     ELOOPI1
STC    R6,PACK(R6)        pack(i)=i
LA     R6,1(R6)           i=i+1
B      LOOPI1
ELOOPI1  LA     R7,CARDS           n=cards
LOOPN    C      R7,=F'2'           do n=cards to 2 by -1
BL     ELOOPN
L      R5,RANDSEED        r5=seed
M      R4,=F'397204094'   r4r5=seed*const
D      R4,=X'7FFFFFFF'    r5=r5 div (2^31-1)
ST     R4,RANDSEED        r4=r5 mod (2^31-1); seed=r4
LR     R5,R4              r5=seed
LA     R4,0               r4=0
DR     R4,R7              r5=seed div n; r4=seed mod n
LA     R9,1(R4)           r2=randint(n)+1 [1:n]
LA     R4,PACK(R7)        @pack(n)
LA     R5,PACK(R9)        @pack(nw)
MVC    TMP,0(R4)          tmp=pack(n)
MVC    0(1,R4),0(R5)      pack(n)=pack(nw)
MVC    0(1,R5),TMP        pack(nw)=tmp
BCTR   R7,0               n=n-1
B      LOOPN
ELOOPN   LA     R6,1               i=1
LA     R8,PG              pgi=@pg
LOOPI2   C      R6,=A(CARDS)       do i=1 to cards
BH     ELOOPI2
XR     R2,R2              r2=0
IC     R2,PACK(R6)        pack(i)
XDECO  R2,XD              edit pack(i)
MVC    0(3,R8),XD+9       output pack(i)
LA     R8,3(R8)           pgi=pgi+3
LA     R6,1(R6)           i=i+1
B      LOOPI2
ELOOPI2  XPRNT  PG,80              print buffer
XR     R15,R15            set return code
CARDS    EQU    20                 number of cards
PACK     DS     (CARDS+1)C         pack of cards
TMP      DS     C                  temp for swap
PG       DC     CL80' '            buffer
XD       DS     CL12               to decimal
RANDSEED DC     F'16807'           running seed
YREGS
END    KNUTHSH
Output:
 13 16 10 18 19 14  6 17  2  5  1 15  7 11 12  9  8 20  4  3


## 6502 Assembly

### When the array address is known before runtime

Runs on easy6502, which has a random number generated memory-mapped at zero page address $FE that updates after every instruction. Works on any array size up to and including 256 bytes. (The code I wrote here prior to this edit was much faster but only worked on arrays of exactly 256 bytes in size). The reason for this was that constraining a random number generator that can produce any 8-bit value to a subset is tricky, since just "rolling again" if out of range will eventually cause the program to lock up if it can't produce a value in range purely by chance. This method uses a bit mask that shifts right as the loop counter decreases to zero, which means that even when only a few bytes still need to be shuffled, the routine is just as quick as it was at the beginning. define sysRandom$fe
define tempMask $ff define range$00
define tempX $01 define tempY$02
define tempRandIndex $03 define temp$04
CreateIdentityTable:
txa
sta $0200,x sta$1000,x
inx
bne CreateIdentityTable
;creates a sorted array from 0-255 starting at addr $1000 ;also creates another one at$0200 for our test input

lda #1
sta range

ConstrainRNG:
ldx #255
;max range of RNG
lda range
bne outerloop
jmp end

outerloop:
cpx range
bcc continue	;if X >= range, we need to lower X
pha
txa
sta tempX

lsr
cmp range
bcc continue2

tax
pla
jmp outerloop

continue2:
pla
ldx tempX

continue:
ldy range

KnuthShuffle:
lda sysRandom
and $1000,x ;and with range constrictor tay lda$0200,y
sty tempRandIndex
sta temp
ldy range
lda $0200,y pha lda temp sta$0200,y
pla
ldy tempRandIndex
sta 0200,y dec range jmp ConstrainRNG end: brk ## AArch64 Assembly Works with: as version Raspberry Pi 3B version Buster 64 bits /* ARM assembly AARCH64 Raspberry PI 3B */ /* program knuthshuffle64.s */ /*******************************************/ /* Constantes file */ /*******************************************/ /* for this file see task include a file in language AArch64 assembly*/ .include "../includeConstantesARM64.inc" /*********************************/ /* Initialized data */ /*********************************/ .data sMessResult: .asciz "Value : @ \n" szCarriageReturn: .asciz "\n" .align 4 TableNumber: .quad 1,2,3,4,5,6,7,8,9,10 .equ NBELEMENTS, (. - TableNumber) / 8 /*********************************/ /* UnInitialized data */ /*********************************/ .bss sZoneConversion: .skip 30 /*********************************/ /* code section */ /*********************************/ .text .global main main: // entry of program ldr x0,qAdrTableNumber // address number table mov x1,NBELEMENTS // number of élements bl knuthShuffle ldr x2,qAdrTableNumber mov x3,0 1: // loop display table ldr x0,[x2,x3,lsl 3] ldr x1,qAdrsZoneConversion // display value bl conversion10S // call function ldr x0,qAdrsMessResult ldr x1,qAdrsZoneConversion bl strInsertAtCharInc bl affichageMess // display message add x3,x3,1 cmp x3,NBELEMENTS - 1 ble 1b ldr x0,qAdrszCarriageReturn bl affichageMess /* 2e shuffle */ ldr x0,qAdrTableNumber // address number table mov x1,NBELEMENTS // number of élements bl knuthShuffle ldr x2,qAdrTableNumber mov x3,0 2: // loop display table ldr x0,[x2,x3,lsl 3] ldr x1,qAdrsZoneConversion // display value bl conversion10S // call function ldr x0,qAdrsMessResult ldr x1,qAdrsZoneConversion bl strInsertAtCharInc bl affichageMess // display message add x3,x3,1 cmp x3,NBELEMENTS - 1 ble 2b 100: // standard end of the program mov x0,0 // return code mov x8,EXIT // request to exit program svc 0 // perform the system call qAdrszCarriageReturn: .quad szCarriageReturn qAdrsMessResult: .quad sMessResult qAdrTableNumber: .quad TableNumber qAdrsZoneConversion: .quad sZoneConversion /******************************************************************/ /* Knuth Shuffle */ /******************************************************************/ /* x0 contains the address of table */ /* x1 contains the number of elements */ knuthShuffle: stp x1,lr,[sp,-16]! // save registers stp x2,x3,[sp,-16]! // save registers stp x4,x5,[sp,-16]! // save registers stp x6,x7,[sp,-16]! // save registers mov x5,x0 // save table address mov x6,x1 // save number of elements mov x2,0 // start index 1: mov x0,0 mov x1,x2 // generate aleas bl extRandom ldr x3,[x5,x2,lsl 3] // swap number on the table ldr x4,[x5,x0,lsl 3] str x4,[x5,x2,lsl 3] str x3,[x5,x0,lsl 3] add x2,x2,1 // next number cmp x2,x6 // end ? blt 1b // no -> loop 100: ldp x6,x7,[sp],16 // restaur 2 registers ldp x4,x5,[sp],16 // restaur 2 registers ldp x2,x3,[sp],16 // restaur 2 registers ldp x1,lr,[sp],16 // restaur 2 registers ret /******************************************************************/ /* random number */ /******************************************************************/ /* x0 contains inferior value */ /* x1 contains maxi value */ /* x0 return random number */ extRandom: stp x1,lr,[sp,-16]! // save registers stp x2,x8,[sp,-16]! // save registers stp x19,x20,[sp,-16]! // save registers sub sp,sp,16 // reserve 16 octets on stack mov x19,x0 add x20,x1,1 mov x0,sp // store result on stack mov x1,8 // length 8 bytes mov x2,0 mov x8,278 // call system Linux 64 bits Urandom svc 0 mov x0,sp // load résult on stack ldr x0,[x0] sub x2,x20,x19 // calculation of the range of values udiv x1,x0,x2 // calculation range modulo msub x0,x1,x2,x0 add x0,x0,x19 // and add inferior value 100: add sp,sp,16 // alignement stack ldp x19,x20,[sp],16 // restaur 2 registers ldp x2,x8,[sp],16 // restaur 2 registers ldp x1,lr,[sp],16 // restaur 2 registers ret // return to address lr x30 /********************************************************/ /* File Include fonctions */ /********************************************************/ /* for this file see task include a file in language AArch64 assembly */ .include "../includeARM64.inc" ## ACL2 :set-state-ok t (defun array-swap (name array i j) (let ((ai (aref1 name array i)) (aj (aref1 name array j))) (aset1 name (aset1 name array j ai) i aj))) (defun shuffle-r (name array m state) (if (zp m) (mv array state) (mv-let (i state) (random m state)
(shuffle-r name
(array-swap name array i m)
(1- m)
state))))

(defun shuffle (name array state)
(shuffle-r name
array
(1- (first (dimensions name array)))
state))


## Action!

PROC PrintTable(INT ARRAY tab BYTE size)
BYTE i

FOR i=0 TO size-1
DO
PrintF("%I ",tab(i))
OD
PutE()
RETURN

PROC KnuthShuffle(INT ARRAY tab BYTE size)
BYTE i,j
INT tmp

i=size-1
WHILE i>0
DO
j=Rand(i+1)
tmp=tab(i)
tab(i)=tab(j)
tab(j)=tmp
i==-1
OD
RETURN

PROC Main()
BYTE i,size=
INT ARRAY tab(size)

FOR i=0 TO size-1
DO
tab(i)=-50+10*i
OD

PrintE("Original data:")
PrintTable(tab,size)
PutE()

KnuthShuffle(tab,size)

PrintE("Shuffled data:")
PrintTable(tab,size)
RETURN
Output:
Original data:
-50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

Shuffled data:
0 60 70 90 80 120 10 50 30 -30 -20 110 -50 140 100 -10 -40 40 20 130


This implementation is a generic shuffle routine, able to shuffle an array of any type.

generic
type Element_Type is private;
type Array_Type is array (Positive range <>) of Element_Type;

procedure Generic_Shuffle (List : in out Array_Type);

with Ada.Numerics.Discrete_Random;

procedure Generic_Shuffle (List : in out Array_Type) is
package Discrete_Random is new Ada.Numerics.Discrete_Random(Result_Subtype => Integer);
use Discrete_Random;
K : Integer;
G : Generator;
T : Element_Type;
begin
Reset (G);
for I in reverse List'Range loop
K := (Random(G) mod I) + 1;
T := List(I);
List(I) := List(K);
List(K) := T;
end loop;
end Generic_Shuffle;


An example using Generic_Shuffle.

with Ada.Text_IO;
with Generic_Shuffle;

procedure Test_Shuffle is

type Integer_Array is array (Positive range <>) of Integer;

Integer_List : Integer_Array
:= (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18);
procedure Integer_Shuffle is new Generic_Shuffle(Element_Type => Integer,
Array_Type => Integer_Array);
begin

for I in Integer_List'Range loop
end loop;
Integer_Shuffle(List => Integer_List);
for I in Integer_List'Range loop
end loop;
end Test_Shuffle;


## Aime

The shuffle function works on any type (the lists are heterogenous).

void
shuffle(list l)
{
integer i;

i = ~l;
if (i) {
i -= 1;
while (i) {
l.spin(i, drand(i));
i -= 1;
}
}
}

## ALGOL 68

Works with: ALGOL 68G
PROC between = (INT a, b)INT :
(
ENTIER (random * ABS (b-a+1) + (a<b|a|b))
);

PROC knuth shuffle = (REF[]INT a)VOID:
(
FOR i FROM LWB a TO UPB a DO
INT j = between(LWB a, UPB a);
INT t = a[i];
a[i] := a[j];
a[j] := t
OD
);
main:(
INT a;
FOR i FROM 1 TO 20 DO a[i] := i OD;
knuth shuffle(a);
print(a)
)

## AppleScript

### Iteration

set n to 25

set array to {}
repeat with i from 1 to n
set end of array to i
end repeat
copy {array, array} to {unshuffled, shuffled}
repeat with i from n to 1 by -1
set j to (((random number) * (i - 1)) as integer) + 1
set shuffled's item i to array's item j
if j ≠ i's contents then set array's item j to array's item i
end repeat

return {unshuffled, shuffled}


Example:

{{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25},
{14, 25, 3, 1, 12, 18, 11, 20, 16, 15, 21, 5, 22, 19, 2, 24, 8, 10, 13, 6, 17, 23, 9, 7, 4}}


Better:

-- Fisher-Yates (aka Durstenfeld, aka Knuth) shuffle.
on shuffle(theList, l, r)
set listLength to (count theList)
if (listLength < 2) then return array
if (l < 0) then set l to listLength + l + 1
if (r < 0) then set r to listLength + r + 1
if (l > r) then set {l, r} to {r, l}
script o
property lst : theList
end script

repeat with i from l to (r - 1)
set j to (random number from i to r)
set v to o's lst's item i
set o's lst's item i to o's lst's item j
set o's lst's item j to v
end repeat

return theList
end shuffle

local array
set array to {"Alpha", "Bravo", "Charlie", "Delta", "Echo", "Foxtrot", "Golf", "Hotel", "India", "Juliett", "Kilo", "Lima", "Mike"}
-- Shuffle all items (1 thru -1).
shuffle(array, 1, -1)

Output:

eg.

{"Golf", "Foxtrot", "Echo", "Delta", "Kilo", "Charlie", "Mike", "Alpha", "Lima", "Juliett", "India", "Bravo", "Hotel"}


When a large number of random indices is required, it can actually be faster to create a list of integers and select from these using AppleScript's 'some' specifier than to call the StandardAdditions' 'random number' function repeatedly. But a better solution since Mac OS X 10.11 is to use the system's GameplayKit framework:

use AppleScript version "2.5" -- OS X 10.11 (El Capitan) or later
use framework "Foundation"
use framework "GameplayKit"

on shuffle(theList, l, r)
set listLength to (count theList)
if (listLength < 2) then return theList
if (l < 0) then set l to listLength + l + 1
if (r < 0) then set r to listLength + r + 1
if (l > r) then set {l, r} to {r, l}
script o
property lst : theList
end script

set rndGenerator to current application's class "GKRandomDistribution"'s distributionWithLowestValue:(l) highestValue:(r)
repeat with i from r to (l + 1) by -1
set j to (rndGenerator's nextIntWithUpperBound:(i))
set v to o's lst's item i
set o's lst's item i to o's lst's item j
set o's lst's item j to v
end repeat

return theList
end shuffle


### Functional composition

-- KNUTH SHUFFLE -------------------------------------------------------------

-- knuthShuffle :: [a] -> [a]
on knuthShuffle(xs)

-- randomSwap :: [Int] -> Int -> [Int]
script randomSwap
on |λ|(a, i)
if i > 1 then
set iRand to random number from 1 to i
tell a
set tmp to item iRand
set item iRand to item i
set item i to tmp
it
end tell
else
a
end if
end |λ|
end script

foldr(randomSwap, xs, enumFromTo(1, length of xs))
end knuthShuffle

-- TEST ----------------------------------------------------------------------
on run
knuthShuffle(["alpha", "beta", "gamma", "delta", "epsilon", ¬
"zeta", "eta", "theta", "iota", "kappa", "lambda", "mu"])
end run

-- GENERIC FUNCTIONS ---------------------------------------------------------

-- enumFromTo :: Int -> Int -> [Int]
on enumFromTo(m, n)
if m > n then
set d to -1
else
set d to 1
end if
set lst to {}
repeat with i from m to n by d
set end of lst to i
end repeat
return lst
end enumFromTo

-- foldr :: (a -> b -> a) -> a -> [b] -> a
on foldr(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with i from lng to 1 by -1
set v to |λ|(v, item i of xs, i, xs)
end repeat
return v
end tell
end foldr

-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn

Output:

e.g.

{"mu", "theta", "alpha", "delta", "zeta", "gamma",
"iota", "kappa", "lambda", "epsilon", "beta", "eta"}


## ARM Assembly

Works with: as version Raspberry Pi
/* ARM assembly Raspberry PI  */
/*  program knuthShuffle.s   */

/************************************/
/* Constantes                       */
/************************************/
.equ STDOUT, 1     @ Linux output console
.equ EXIT,   1     @ Linux syscall
.equ WRITE,  4     @ Linux syscall
/*********************************/
/* Initialized data              */
/*********************************/
.data
sMessResult:      .ascii "Value  : "
sMessValeur:       .fill 11, 1, ' '            @ size => 11
szCarriageReturn: .asciz "\n"

.align 4
iGraine:  .int 123456
.equ NBELEMENTS,      10
TableNumber:	     .int   1,2,3,4,5,6,7,8,9,10

/*********************************/
/* UnInitialized data            */
/*********************************/
.bss
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main
main:                                           @ entry of program
mov r1,#NBELEMENTS                          @ number of élements
bl knuthShuffle
mov r3,#0
1:                                              @ loop display table
ldr r0,[r2,r3,lsl #2]
bl conversion10                             @ call function
bl affichageMess                            @ display message
cmp r3,#NBELEMENTS - 1
ble 1b

bl affichageMess
/*    2e shuffle             */
mov r1,#NBELEMENTS                         @ number of élements
bl knuthShuffle
mov r3,#0
2:                                             @ loop display table
ldr r0,[r2,r3,lsl #2]
bl conversion10                            @ call function
bl affichageMess                           @ display message
cmp r3,#NBELEMENTS - 1
ble 2b

100:                                            @ standard end of the program
mov r0, #0                                  @ return code
mov r7, #EXIT                               @ request to exit program
svc #0                                      @ perform the system call

/******************************************************************/
/*     Knuth Shuffle                                             */
/******************************************************************/
/* r0 contains the address of table */
/* r1 contains the number of elements */
knuthShuffle:
push {r2-r5,lr}                                    @ save registers
mov r5,r0                                          @ save table address
mov r2,#0                                          @ start index
1:
mov r0,r2                                          @ generate aleas
bl genereraleas
ldr r3,[r5,r2,lsl #2]                              @ swap number on the table
ldr r4,[r5,r0,lsl #2]
str r4,[r5,r2,lsl #2]
str r3,[r5,r0,lsl #2]
cmp r2,r1                                           @ end ?
blt 1b                                              @ no -> loop

100:
pop {r2-r5,lr}
bx lr                                               @ return

/******************************************************************/
/*     display text with size calculation                         */
/******************************************************************/
/* r0 contains the address of the message */
affichageMess:
push {r0,r1,r2,r7,lr}                          @ save  registres
mov r2,#0                                      @ counter length
1:                                                 @ loop length calculation
ldrb r1,[r0,r2]                                @ read octet start position + index
cmp r1,#0                                      @ if 0 its over
bne 1b                                         @ and loop
@ so here r2 contains the length of the message
mov r1,r0                                      @ address message in r1
mov r0,#STDOUT                                 @ code to write to the standard output Linux
mov r7, #WRITE                                 @ code call system "write"
svc #0                                         @ call systeme
pop {r0,r1,r2,r7,lr}                           @ restaur des  2 registres */
bx lr                                          @ return
/******************************************************************/
/*     Converting a register to a decimal unsigned                */
/******************************************************************/
/* r0 contains value and r1 address area   */
/* r0 return size of result (no zero final in area) */
/* area size => 11 bytes          */
.equ LGZONECAL,   10
conversion10:
push {r1-r4,lr}                                @ save registers
mov r3,r1
mov r2,#LGZONECAL

1:	                                           @ start loop
bl divisionpar10U                              @unsigned  r0 <- dividende. quotient ->r0 reste -> r1
strb r1,[r3,r2]                                @ store digit on area
cmp r0,#0                                      @ stop if quotient = 0
subne r2,#1                                    @ else previous position
bne 1b	                                   @ and loop
@ and move digit from left of area
mov r4,#0
2:
ldrb r1,[r3,r2]
strb r1,[r3,r4]
cmp r2,#LGZONECAL
ble 2b
@ and move spaces in end on area
mov r0,r4                                         @ result length
mov r1,#' '                                       @ space
3:
strb r1,[r3,r4]                                   @ store space in area
cmp r4,#LGZONECAL
ble 3b                                            @ loop if r4 <= area size

100:
pop {r1-r4,lr}                                    @ restaur registres
bx lr                                             @return

/***************************************************/
/*   division par 10   unsigned                    */
/***************************************************/
/* r0 dividende   */
/* r0 quotient */
/* r1 remainder  */
divisionpar10U:
push {r2,r3,r4, lr}
mov r4,r0                                          @ save value
//mov r3,#0xCCCD                                   @ r3 <- magic_number lower  raspberry 3
//movt r3,#0xCCCC                                  @ r3 <- magic_number higter raspberry 3
ldr r3,iMagicNumber                                @ r3 <- magic_number    raspberry 1 2
umull r1, r2, r3, r0                               @ r1<- Lower32Bits(r1*r0) r2<- Upper32Bits(r1*r0)
mov r0, r2, LSR #3                                 @ r2 <- r2 >> shift 3
add r2,r0,r0, lsl #2                               @ r2 <- r0 * 5
sub r1,r4,r2, lsl #1                               @ r1 <- r4 - (r2 * 2)  = r4 - (r0 * 10)
pop {r2,r3,r4,lr}
bx lr                                              @ leave function
iMagicNumber:  	.int 0xCCCCCCCD
/***************************************************/
/*   Generation random number                  */
/***************************************************/
/* r0 contains limit  */
genereraleas:
push {r1-r4,lr}                                    @ save registers
ldr r2,[r4]
ldr r3,iNbDep1
mul r2,r3,r2
ldr r3,iNbDep1
str r2,[r4]                                        @ maj de la graine pour l appel suivant
cmp r0,#0
beq 100f
mov r1,r0                                          @ divisor
mov r0,r2                                          @ dividende
bl division
mov r0,r3                                          @ résult = remainder

100:                                                   @ end function
pop {r1-r4,lr}                                     @ restaur registers
bx lr                                              @ return
/*****************************************************/
iNbDep1: .int 0x343FD
iNbDep2: .int 0x269EC3
/***************************************************/
/* integer division unsigned                       */
/***************************************************/
division:
/* r0 contains dividend */
/* r1 contains divisor */
/* r2 returns quotient */
/* r3 returns remainder */
push {r4, lr}
mov r2, #0                                         @ init quotient
mov r3, #0                                         @ init remainder
mov r4, #32                                        @ init counter bits
b 2f
1:                                                     @ loop
movs r0, r0, LSL #1                                @ r0 <- r0 << 1 updating cpsr (sets C if 31st bit of r0 was 1)
adc r3, r3, r3                                     @ r3 <- r3 + r3 + C. This is equivalent to r3 ? (r3 << 1) + C
cmp r3, r1                                         @ compute r3 - r1 and update cpsr
subhs r3, r3, r1                                   @ if r3 >= r1 (C=1) then r3 <- r3 - r1
adc r2, r2, r2                                     @ r2 <- r2 + r2 + C. This is equivalent to r2 <- (r2 << 1) + C
2:
subs r4, r4, #1                                    @ r4 <- r4 - 1
bpl 1b                                             @ if r4 >= 0 (N=0) then loop
pop {r4, lr}
bx lr

## Arturo

knuth: function [arr][
if 0=size arr -> return []

loop ((size arr)-1)..0 'i [
j: random 0 i

tmp: arr\[i]
set arr i arr\[j]
set arr j tmp
]

return arr
]

print knuth []
print knuth 
print knuth [10 20]
print knuth [10 20 30]


## AutoHotkey

ahk forum: discussion

MsgBox % shuffle("1,2,3,4,5,6,7,8,9")
MsgBox % shuffle("1,2,3,4,5,6,7,8,9")

shuffle(list) {                          ; shuffle comma separated list, converted to array
StringSplit a, list, ,               ; make array (length = a0)
Loop % a0-1 {
Random i, A_Index, a0              ; swap item 1,2... with a random item to the right of it
t := a%i%, a%i% := a%A_Index%, a%A_Index% := t
}
Loop % a0                             ; construct string from sorted array
s .= "," . a%A_Index%
Return SubStr(s,2)                    ; drop leading comma
}


For Arrays:

toShuffle:=[1,2,3,4,5,6]
shuffled:=shuffle(toShuffle)
;p(toShuffle) ;because it modifies the original array
;or
;p(shuffled)
shuffle(a)
{
i := a.Length()
loop % i-1 {
Random, j,1,% i
x := a[i]
a[i] := a[j]
a[j] := x
i--
}
return a
}


## AutoIt

Dim $a ConsoleWrite('array before permutation:' & @CRLF) For$i = 0 To 9
$a[$i] = Random(20,100,1)
ConsoleWrite($a[$i] & ' ')
Next
ConsoleWrite(@CRLF)

_Permute($a) ConsoleWrite('array after permutation:' & @CRLF) For$i = 0 To UBound($a) -1 ConsoleWrite($a[$i] & ' ') Next ConsoleWrite(@CRLF) Func _Permute(ByRef$array)
Local $random,$tmp
For $i = UBound($array) -1 To 0 Step -1
$random = Random(0,$i,1)
$tmp =$array[$random]$array[$random] =$array[$i]$array[$i] =$tmp
Next
EndFunc

Output:
 array before permutation:
43 57 37 20 97 98 69 76 97 70
array after permutation:
57 69 97 70 37 97 20 76 43 98


## AWK

Many arrays in AWK have the first index at 1. This example shows how to shuffle such arrays. The elements can be integers, floating-point numbers, or strings.

# Shuffle an _array_ with indexes from 1 to _len_.
function shuffle(array, len,    i, j, t) {
for (i = len; i > 1; i--) {
# j = random integer from 1 to i
j = int(i * rand()) + 1

# swap array[i], array[j]
t = array[i]
array[i] = array[j]
array[j] = t
}
}

# Test program.
BEGIN {
len = split("11 22 33 44 55 66 77 88 99 110", array)
shuffle(array, len)

for (i = 1; i < len; i++) printf "%s ", array[i]
printf "%s\n", array[len]
}


## BASIC

RANDOMIZE TIMER

DIM cards(51) AS INTEGER
DIM L0 AS LONG, card AS LONG

PRINT "before:"
FOR L0 = 0 TO 51
cards(L0) = L0
PRINT LTRIM$(STR$(cards(L0))); " ";
NEXT

FOR L0 = 51 TO 0 STEP -1
card = INT(RND * (L0 + 1))
IF card <> L0 THEN SWAP cards(card), cards(L0)
NEXT

PRINT : PRINT "after:"
FOR L0 = 0 TO 51
PRINT LTRIM$(STR$(cards(L0))); " ";
NEXT
PRINT

Output:
 before:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
after:
27 14 37 35 3 44 25 38 46 1 22 49 2 51 16 32 20 30 4 33 36 6 31 21 41 34 9 13 0
50 47 48 40 39 7 18 19 26 24 10 29 5 12 28 11 17 43 45 8 23 42 15


### Applesoft BASIC

As mentioned in the Sinclair ZX81 BASIC solution, for very small positive integer values, a string is a much more memory-efficient array, but here is an example of an array with numbers. Line 150 initializes and prints each element in the array. Line 190 performs the swap of the elements.

 100 :
110  REM  KNUTH SHUFFLE
120 :
130  DIM A(25)
140  FOR I = 1 TO 25
150 A(I) = I: PRINT A(I);" ";: NEXT I
160  PRINT : PRINT
170  FOR I = 25 TO 2 STEP  - 1
180 J =  INT ( RND (1) * I + 1)
190 T = A(I):A(I) = A(J):A(J) = T: NEXT I
200  FOR I = 1 TO 25
210  PRINT A(I);" ";: NEXT I
220  END

Output:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1
7 18 19 20 21 22 23 24 25

When it has finished, the screen will show (for example):

20 5 6 9 15 23 22 8 4 24 7 11 16 21 2 17
14 10 19 13 12 18 1 3 25

### BBC BASIC

      cards% = 52
DIM pack%(cards%)
FOR I% = 1 TO cards%
pack%(I%) = I%
NEXT I%
FOR N% = cards% TO 2 STEP -1
SWAP pack%(N%),pack%(RND(N%))
NEXT N%
FOR I% = 1 TO cards%
PRINT pack%(I%);
NEXT I%
PRINT


### IS-BASIC

100 PROGRAM "Shuffle.bas"
110 RANDOMIZE
120 NUMERIC ARRAY(1 TO 20)
130 CALL INIT(ARRAY)
140 CALL WRITE(ARRAY)
150 CALL SHUFFLE(ARRAY)
160 CALL WRITE(ARRAY)
170 DEF INIT(REF A)
180   FOR I=LBOUND(A) TO UBOUND(A)
190     LET A(I)=I
200   NEXT
210 END DEF
220 DEF WRITE(REF A)
230   FOR I=LBOUND(A) TO UBOUND(A)
240     PRINT A(I);
250   NEXT
260   PRINT
270 END DEF
280 DEF SHUFFLE(REF A)
290   FOR I=UBOUND(A) TO LBOUND(A) STEP-1
300     LET CARD=RND(UBOUND(A)-LBOUND(A))+LBOUND(A)+1
310     IF CARD<>I THEN LET T=A(CARD):LET A(CARD)=A(I):LET A(I)=T
320   NEXT
330 END DEF

### OxygenBasic

uses chaos
uses timeutil
seed=GetTickCount
int i,j
int d 'int array or any other type
...
for i=100 to 1 step -1
j=irnd(1,100)
swap d[i],d[j]
next


### QB64

Shuffle and make sure that number does not take its place
and between cells at least 10% ... Shuffle from Russia

a = 100: DIM d(a): x=0: k=0: t$=CHR$(9): RANDOMIZE TIMER 'Shuffle_RUS.bas
PRINT ,: FOR i = 1 TO a: d(i)=i: NEXT
FOR i = 1 TO 5: PRINT d(i);: NEXT: PRINT ,
FOR i = a-3 TO a: PRINT d(i);: NEXT: z = TIMER
OPEN "b:/control.txt" FOR OUTPUT AS #1 ' ram disk
WHILE x < 1
v = 0: FOR i = 1 TO a
1 m = INT(RND*a)+1: IF ABS(d(i)-d(m)) < .1*a THEN v = v+1: GOTO 1
PRINT #1, ABS(d(i)-d(m)); t$; d(i); t$; d(m); t$; i; t$; m; t$; d(i)/d(m); t$; d(m)/d(i) ' ram disk
t = d(i): d(i) = d(m): d(m) = t
NEXT

s = 0: FOR i = 1 TO a
IF d(i) = i THEN s = s+1 ' : goto 5
NEXT
5 k = k+1: PRINT: PRINT s; v,: IF s=0 THEN x = x+1

FOR i = 1 TO 5
IF d(i) = i THEN PRINT -d(i); ELSE PRINT d(i);
NEXT: PRINT ,
FOR i = a-3 TO a
IF d(i) = i THEN PRINT -d(i); ELSE PRINT d(i);
NEXT
WEND: PRINT: PRINT "    = "; k, TIMER-z: END


### Sinclair ZX81 BASIC

For very small positive integer values, a string (which can be treated as an array of bytes) is much more memory-efficient than an array of numbers. In this program we shuffle a string consisting of the letters 'A' to 'Z'. The ZX81 is slow enough that we can watch the shuffle happening in real time, with items switching to inverse video display as they are shuffled. (This can be done, in the ZX81 character set, by setting the high bit in the character code.) Line 10 seeds the pseudo-random number generator. Note that strings (and arrays) are indexed from 1.

The program works with the unexpanded (1k RAM) ZX81.

 10 RAND
20 LET A$="" 30 FOR I=1 TO 26 40 LET A$=A$+CHR$ (37+I)
50 NEXT I
60 PRINT A$70 FOR I=26 TO 2 STEP -1 80 LET J=1+INT (RND*I) 90 LET T$=A$(I) 100 LET A$(I)=A$(J) 110 LET A$(J)=T$120 PRINT AT 0,I-1;CHR$ (CODE A$(I)+128) 130 PRINT AT 0,J-1;CHR$ (CODE A$(J)+128) 140 NEXT I  Output: While the program is running, we will see something like this (using lower case as a stand-in for inverse video): ABCuEFGzwJKLMNOPxySvdtiqrh When it has finished, the screen will show (for example): lcjbpxekzsaygumwnovfdtiqrh ### True BASIC Translation of: BASIC OPTION BASE 0 RANDOMIZE DIM cards(51) PRINT "before:" FOR L0 = 0 TO 51 LET cards(L0) = L0 PRINT LTRIM$(STR$(cards(L0))); " "; NEXT L0 FOR L0 = 51 TO 0 STEP -1 LET card = INT(RND * (L0 + 1)) IF card <> L0 THEN LET t = cards(lb + L0) LET cards(lb + L0) = cards(lb + card) LET cards(lb + card) = t END IF NEXT L0 PRINT PRINT "after:" FOR L0 = 0 TO 51 PRINT LTRIM$(STR$(cards(L0))); " "; NEXT L0 END  Output: Same as BASIC entry. ## bc I provide a shuffle() function. It can only shuffle an array of numbers. It fails if the array has more than 32768 elements. It always shuffles the array named shuffle[]; the array is not a function parameter because bc passes arrays by copying. This code requires a bc with long names; the test program also requires a bc with the print statement. Works with: OpenBSD bc seed = 1 /* seed of the random number generator */ scale = 0 /* Random number from 0 to 32767. */ define rand() { /* Formula (from POSIX) for random numbers of low quality. */ seed = (seed * 1103515245 + 12345) % 4294967296 return ((seed / 65536) % 32768) } /* Shuffle the first _count_ elements of shuffle[]. */ define shuffle(count) { auto b, i, j, t i = count while (i > 0) { /* j = random number in [0, i) */ b = 32768 % i /* want rand() >= b */ while (1) { j = rand() if (j >= b) break } j = j % i /* decrement i, swap shuffle[i] and shuffle[j] */ t = shuffle[--i] shuffle[i] = shuffle[j] shuffle[j] = t } } /* Test program. */ define print_array(count) { auto i for (i = 0; i < count - 1; i++) print shuffle[i], ", " print shuffle[i], "\n" } for (i = 0; i < 10; i++) shuffle[i] = 11 * (i + 1) "Original array: "; trash = print_array(10) trash = shuffle(10) "Shuffled array: "; trash = print_array(10) quit  Output: Original array: 11, 22, 33, 44, 55, 66, 77, 88, 99, 110 Shuffled array: 66, 44, 11, 55, 33, 77, 110, 22, 88, 99 ## BQN BQN's arrays are immutable, but variable values can be changed using the ↩ symbol. This program repeatedly changes the array's value using under. Knuth ← { 𝕊 arr: l ← ≠arr { arr ↩ ⌽⌾(⟨•rand.Range l, 𝕩⟩⊸⊏)arr }¨↕l arr } P ← •Show Knuth P ⟨⟩ P ⟨10⟩ P ⟨10, 20⟩ P ⟨10, 20, 30⟩ ## Brat shuffle = { a | (a.length - 1).to 1 { i | random_index = random(0, i) temp = a[i] a[i] = a[random_index] a[random_index] = temp } a } p shuffle [1 2 3 4 5 6 7] ## C This shuffles any "object"; it imitates qsort in the syntax. #include <stdlib.h> #include <string.h> int rrand(int m) { return (int)((double)m * ( rand() / (RAND_MAX+1.0) )); } #define BYTE(X) ((unsigned char *)(X)) void shuffle(void *obj, size_t nmemb, size_t size) { void *temp = malloc(size); size_t n = nmemb; while ( n > 1 ) { size_t k = rrand(n--); memcpy(temp, BYTE(obj) + n*size, size); memcpy(BYTE(obj) + n*size, BYTE(obj) + k*size, size); memcpy(BYTE(obj) + k*size, temp, size); } free(temp); }  Alternatively, using Durstenfeld's method (swapping selected item and last item in each iteration instead of literally shifting everything), and macro'd function declaration/definition: #include <stdio.h> #include <stdlib.h> /* define a shuffle function. e.g. decl_shuffle(double). * advantage: compiler is free to optimize the swap operation without * indirection with pointers, which could be much faster. * disadvantage: each datatype needs a separate instance of the function. * for a small funciton like this, it's not very big a deal. */ #define decl_shuffle(type) \ void shuffle_##type(type *list, size_t len) { \ int j; \ type tmp; \ while(len) { \ j = irand(len); \ if (j != len - 1) { \ tmp = list[j]; \ list[j] = list[len - 1]; \ list[len - 1] = tmp; \ } \ len--; \ } \ } \ /* random integer from 0 to n-1 */ int irand(int n) { int r, rand_max = RAND_MAX - (RAND_MAX % n); /* reroll until r falls in a range that can be evenly * distributed in n bins. Unless n is comparable to * to RAND_MAX, it's not *that* important really. */ while ((r = rand()) >= rand_max); return r / (rand_max / n); } /* declare and define int type shuffle function from macro */ decl_shuffle(int); int main() { int i, x; for (i = 0; i < 20; i++) x[i] = i; for (printf("before:"), i = 0; i < 20 || !printf("\n"); i++) printf(" %d", x[i]); shuffle_int(x, 20); for (printf("after: "), i = 0; i < 20 || !printf("\n"); i++) printf(" %d", x[i]); return 0; }  ## C# public static void KnuthShuffle<T>(T[] array) { System.Random random = new System.Random(); for (int i = 0; i < array.Length; i++) { int j = random.Next(i, array.Length); // Don't select from the entire array on subsequent loops T temp = array[i]; array[i] = array[j]; array[j] = temp; } }  ## C++ Compiler: g++ (version 4.3.2 20081105 (Red Hat 4.3.2-7)) #include <cstdlib> #include <algorithm> #include <iterator> template<typename RandomAccessIterator> void knuthShuffle(RandomAccessIterator begin, RandomAccessIterator end) { for(unsigned int n = end - begin - 1; n >= 1; --n) { unsigned int k = rand() % (n + 1); if(k != n) { std::iter_swap(begin + k, begin + n); } } }  The standard library provides this in the form of std::random_shuffle. #include <algorithm> #include <vector> int main() { int array[] = { 1,2,3,4,5,6,7,8,9 }; // C-style array of integers std::vector<int> vec(array, array + 9); // build STL container from int array std::random_shuffle(array, array + 9); // shuffle C-style array std::random_shuffle(vec.begin(), vec.end()); // shuffle STL container }  ## Clojure (defn shuffle [vect] (reduce (fn [v i] (let [r (rand-int i)] (assoc v i (v r) r (v i)))) vect (range (dec (count vect)) 1 -1)))  This works by generating a sequence of end-indices from n-1 to 1, then reducing that sequence (starting with the original vector) through a function that, given a vector and end-index, performs a swap between the end-index and some random index less than the end-index. ## CLU knuth_shuffle = proc [T: type] (a: array[T]) lo: int := array[T]$low(a)
hi: int := array[T]$high(a) for i: int in int$from_to_by(hi, lo+1, -1) do
j: int := lo + random$next(i-lo+1) temp: T := a[i] a[i] := a[j] a[j] := temp end end knuth_shuffle start_up = proc () po: stream := stream$primary_output()
d: date := now()
random$seed(d.second + 60*(d.minute + 60*d.hour)) arr: array[int] := array[int]$[1,2,3,4,5,6,7,8,9]
knuth_shuffle[int](arr)
for i: int in array[int]$elements(arr) do stream$puts(po, int$unparse(i) || " ") end end start_up Output: 7 9 2 3 4 8 1 6 5 (Or any other order.) ## CMake # shuffle(<output variable> [<value>...]) shuffles the values, and # stores the result in a list. function(shuffle var) set(forever 1) # Receive ARGV1, ARGV2, ..., ARGV${last} as an array of values.
math(EXPR last "${ARGC} - 1") # Shuffle the array with Knuth shuffle (Fisher-Yates shuffle). foreach(i RANGE${last} 1)
# Roll j = a random number from 1 to i.
math(EXPR min "100000000 % ${i}") while(forever) string(RANDOM LENGTH 8 ALPHABET 0123456789 j) if(NOT j LESS min) # Prevent modulo bias when j < min. break() # Break loop when j >= min. endif() endwhile() math(EXPR j "${j} % ${i} + 1") # Swap ARGV${i} with ARGV${j}. set(t${ARGV${i}}) set(ARGV${i} ${ARGV${j}})
set(ARGV${j}${t})
endforeach(i)

# Convert array to list.
foreach(i RANGE 1 ${last}) list(APPEND answer${ARGV${i}}) endforeach(i) set("${var}" ${answer} PARENT_SCOPE) endfunction(shuffle)  shuffle(result 11 22 33 44 55 66) message(STATUS "${result}")
# One possible output:
# -- 66;33;22;55;44;11


## COBOL

       IDENTIFICATION DIVISION.
PROGRAM-ID. knuth-shuffle.

DATA DIVISION.
LOCAL-STORAGE SECTION.
01  i                       PIC 9(8).
01  j                       PIC 9(8).

01  temp                    PIC 9(8).

78  Table-Len               VALUE 10.
01  ttable-area.
03  ttable              PIC 9(8) OCCURS Table-Len TIMES.

PROCEDURE DIVISION USING ttable-area.
MOVE FUNCTION RANDOM(FUNCTION CURRENT-DATE (11:6)) TO i

PERFORM VARYING i FROM Table-Len BY -1 UNTIL i = 0
COMPUTE j =
FUNCTION MOD(FUNCTION RANDOM * 10000, Table-Len) + 1

MOVE ttable (i) TO temp
MOVE ttable (j) TO ttable (i)
MOVE temp TO ttable (j)
END-PERFORM

GOBACK
.


## CoffeeScript

Translation of: JavaScript
knuth_shuffle = (a) ->
n = a.length
while n > 1
r = Math.floor(n * Math.random())
n -= 1
[a[n], a[r]] = [a[r], a[n]]
a

counts =
"1,2,3": 0
"1,3,2": 0
"2,1,3": 0
"2,3,1": 0
"3,1,2": 0
"3,2,1": 0

for i in [1..100000]
counts[knuth_shuffle([ 1, 2, 3 ]).join(",")] += 1

for key, val of counts
console.log "#{key}: #{val}"

Output:
> coffee knuth_shuffle.coffee
1,2,3: 16714
1,3,2: 16566
2,1,3: 16460
2,3,1: 16715
3,1,2: 16750
3,2,1: 16795


## Common Lisp

(defun nshuffle (sequence)
(loop for i from (length sequence) downto 2
do (rotatef (elt sequence (random i))
(elt sequence (1- i))))
sequence)


This operates on arbitrary sequences, but will be inefficient applied to a list as opposed to a vector. Dispatching on type, and using an intermediate vector to hold the contents of list can make both cases more efficient (since the array specific case can use aref rather than elt):

(defun nshuffle (sequence)
(etypecase sequence
(list  (nshuffle-list sequence))
(array (nshuffle-array sequence))))

(defun nshuffle-list (list)
"Shuffle the list using an intermediate vector."
(let ((array (nshuffle-array (coerce list 'vector))))
(declare (dynamic-extent array))
(map-into list 'identity array)))

(defun nshuffle-array (array)
(loop for i from (length array) downto 2
do (rotatef (aref array (random i))
(aref array (1- i)))
finally (return array)))


## Crystal

def knuthShuffle(items : Array)
i = items.size-1
while i > 1
j = Random.rand(0..i)
items.swap(i, j)

i -= 1
end
end


## D

### Standard Version

A variant of the Knuth shuffle is in the D standard library Phobos:

void main() {
import std.stdio, std.random;

auto a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
a.randomShuffle;
a.writeln;
}

Output:
[8, 9, 3, 1, 7, 5, 4, 6, 2]

### One Implementation

This shuffles any collection that supports random access, length and swapping of items:

import std.stdio, std.algorithm, std.random, std.range;

void knuthShuffle(Range)(Range r)
if (isRandomAccessRange!Range && hasLength!Range &&
hasSwappableElements!Range) {
foreach_reverse (immutable i, ref ri; r[1 .. $- 1]) ri.swap(r[uniform(0, i + 1)]); } void main() { auto a = [1, 2, 3, 4, 5, 6, 7, 8, 9]; a.knuthShuffle; a.writeln; }  ## Delphi See Pascal or DWScript ## DWScript procedure KnuthShuffle(a : array of Integer); var i, j, tmp : Integer; begin for i:=a.High downto 1 do begin j:=RandomInt(a.Length); tmp:=a[i]; a[i]:=a[j]; a[j]:=tmp; end; end;  ## E def shuffle(array, random) { for bound in (2..(array.size())).descending() { def i := random.nextInt(bound) def swapTo := bound - 1 def t := array[swapTo] array[swapTo] := array[i] array[i] := t } } ? def arr := [1,2,3,4,5,6,7,8,9,10].diverge() # value: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].diverge() ? shuffle(arr, entropy) ? arr # value: [4, 5, 2, 9, 7, 8, 1, 3, 6, 10].diverge() ## EasyLang func shuffle . a[] . for i = len a[] downto 2 r = random i swap a[r] a[i] . . arr[] = [ 1 2 3 ] call shuffle arr[] print arr[]  ## EchoLisp Remark- The native '''shuffle''' function implementation in EchoLisp has been replaced by this one. Thx Rosetta Code. (lib 'list) ;; for list-permute ;; use "inside-out" algorithm, no swapping needed. ;; returns a random permutation vector of [0 .. n-1] (define (rpv n (j)) (define v (make-vector n)) (for [(i n)] (set! j (random (1+ i))) (when (!= i j) (vector-set! v i [v j])) (vector-set! v j i)) v) ;; apply to any kind of list (define (k-shuffle list) (list-permute list (vector->list (rpv (length list))))) ;; out (k-shuffle (iota 17)) → (16 7 11 10 0 9 15 12 13 8 4 2 14 3 6 5 1) (k-shuffle '(adrien 🎸 alexandre 🚂 antoine 🍼 ben 📚 georges 📷 julie 🎥 marine 🐼 nathalie 🍕 )) → (marine alexandre 🎥 julie 🎸 ben 🍼 nathalie 📚 georges 🚂 antoine adrien 🐼 📷 🍕) (shuffle ;; native '(adrien 🎸 alexandre 🚂 antoine 🍼 ben 📚 georges 📷 julie 🎥 marine 🐼 nathalie 🍕 )) → (antoine 🎥 🚂 marine adrien nathalie 🍼 🍕 ben 🐼 julie 📷 📚 🎸 alexandre georges)  ## Egel import "prelude.eg" import "random.ego" using System using List using Math def swap = [ I J XX -> insert I (nth J XX) (insert J (nth I XX) XX) ] def shuffle = [ XX -> let INDICES = reverse (fromto 0 ((length XX) - 1)) in let SWAPS = map [ I -> I (between 0 I) ] INDICES in foldr [I J -> swap I J] XX SWAPS ] def main = shuffle (fromto 1 9) ## Eiffel class APPLICATION create make feature {NONE} -- Initialization make do test := <<1, 2>> io.put_string ("Initial: ") across test as t loop io.put_string (t.item.out + " ") end test := shuffle (test) io.new_line io.put_string ("Shuffled: ") across test as t loop io.put_string (t.item.out + " ") end end test: ARRAY [INTEGER] shuffle (ar: ARRAY [INTEGER]): ARRAY [INTEGER] -- Array containing the same elements as 'ar' in a shuffled order. require more_than_one_element: ar.count > 1 local count, j, ith: INTEGER random: V_RANDOM do create random create Result.make_empty Result.deep_copy (ar) count := ar.count across 1 |..| count as c loop j := random.bounded_item (c.item, count) ith := Result [c.item] Result [c.item] := Result [j] Result [j] := ith random.forth end ensure same_elements: across ar as a all Result.has (a.item) end end end  Output: Initial: 1 2 3 4 5 6 7 Shuffeld: 1 5 3 4 7 6 2  ## Elena ELENA 4.x: import system'routines; import extensions; const int MAX = 10; extension randomOp { randomize() { var max := self.Length; for(int i := 0, i < max, i += 1) { var j := randomGenerator.eval(i,max); self.exchange(i,j) }; ^ self } } public program() { var a := Array.allocate:MAX.populate:(i => i ); console.printLine(a.randomize()) } Output: 7,3,6,8,4,9,0,1,2,5  ## Elixir Translation of: Erlang defmodule Knuth do def shuffle( inputs ) do n = length( inputs ) {[], acc} = Enum.reduce( n..1, {inputs, []}, &random_move/2 ) acc end defp random_move( n, {inputs, acc} ) do item = Enum.at( inputs, :rand.uniform(n)-1 ) {List.delete( inputs, item ), [item | acc]} end end seq = Enum.to_list( 0..19 ) IO.inspect Knuth.shuffle( seq ) seq = [1,2,3] Enum.reduce(1..100000, Map.new, fn _,acc -> k = Knuth.shuffle(seq) Map.update(acc, k, 1, &(&1+1)) end) |> Enum.each(fn {k,v} -> IO.inspect {k,v} end)  Output: [17, 13, 4, 2, 16, 1, 8, 19, 9, 12, 14, 5, 0, 11, 6, 10, 18, 3, 15, 7] {[1, 2, 3], 16702} {[1, 3, 2], 16635} {[2, 1, 3], 16518} {[2, 3, 1], 16935} {[3, 1, 2], 16500} {[3, 2, 1], 16710}  ## Erlang -module( knuth_shuffle ). -export( [list/1] ). list( Inputs ) -> N = erlang:length( Inputs ), {[], Acc} = lists:foldl( fun random_move/2, {Inputs, []}, lists:reverse(lists:seq(1, N)) ), Acc. random_move( N, {Inputs, Acc} ) -> Item = lists:nth( random:uniform(N), Inputs ), {lists:delete(Item, Inputs), [Item | Acc]}.  Output: 21> knuth_shuffle:list(lists:seq(1,9)). [5,7,8,1,4,2,3,9,6]  ## ERRE PROGRAM KNUTH_SHUFFLE CONST CARDS%=52 DIM PACK%[CARDS%] BEGIN RANDOMIZE(TIMER) FOR I%=1 TO CARDS% DO PACK%[I%]=I% END FOR FOR N%=CARDS% TO 2 STEP -1 DO SWAP(PACK%[N%],PACK%[1+INT(N%*RND(1))]) END FOR FOR I%=1 TO CARDS% DO PRINT(PACK%[I%];) END FOR PRINT END PROGRAM ## Euphoria Translation of: BASIC sequence cards cards = repeat(0,52) integer card,temp puts(1,"Before:\n") for i = 1 to 52 do cards[i] = i printf(1,"%d ",cards[i]) end for for i = 52 to 1 by -1 do card = rand(i) if card != i then temp = cards[card] cards[card] = cards[i] cards[i] = temp end if end for puts(1,"\nAfter:\n") for i = 1 to 52 do printf(1,"%d ",cards[i]) end for ## F# Allows a shuffle of arrays of arbitrary items. Requires 2010 beta of F#. Lazily returns a sequence. This is the original Fisher-Yates shuffle as described by the link: open System let FisherYatesShuffle (initialList : array<'a>) = // ' let availableFlags = Array.init initialList.Length (fun i -> (i, true)) // Which items are available and their indices let rnd = new Random() let nextItem nLeft = let nItem = rnd.Next(0, nLeft) // Index out of available items let index = // Index in original deck availableFlags // Go through available array |> Seq.filter (fun (ndx,f) -> f) // and pick out only the available tuples |> Seq.nth nItem // Get the one at our chosen index |> fst // and retrieve it's index into the original array availableFlags.[index] <- (index, false) // Mark that index as unavailable initialList.[index] // and return the original item seq {(initialList.Length) .. -1 .. 1} // Going from the length of the list down to 1 |> Seq.map (fun i -> nextItem i) // yield the next item  Here's the modified Knuth shuffle which shuffles the original array in place let KnuthShuffle (lst : array<'a>) = // ' let Swap i j = // Standard swap let item = lst.[i] lst.[i] <- lst.[j] lst.[j] <- item let rnd = new Random() let ln = lst.Length [0..(ln - 2)] // For all indices except the last |> Seq.iter (fun i -> Swap i (rnd.Next(i, ln))) // swap th item at the index with a random one following it (or itself) lst // Return the list shuffled in place  Example: > KnuthShuffle [| "Darrell"; "Marvin"; "Doug"; "Greg"; "Sam"; "Ken" |];; val it : string array = [|"Marvin"; "Doug"; "Sam"; "Darrell"; "Ken"; "Greg"|]  ## Factor There is a randomize word already in the standard library. Implementation: : randomize ( seq -- seq ) dup length [ dup 1 > ] [ [ iota random ] [ 1 - ] bi [ pick exchange ] keep ] while drop ;  ## Fantom class Main { static Void knuthShuffle (List array) { ((array.size-1)..1).each |Int i| { r := Int.random(0..i) array.swap (i, r) } } public static Void main () { List a := [1,2,3,4,5] knuthShuffle (a) echo (a) List b := ["apples", "oranges", "pears", "bananas"] knuthShuffle (b) echo (b) } } ## Forth include random.fs : shuffle ( deck size -- ) 2 swap do dup i random cells + over @ over @ swap rot ! over ! cell+ -1 +loop drop ; : .array 0 do dup @ . cell+ loop drop ; create deck 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , deck 10 2dup shuffle .array  ## Fortran Works with: Fortran version 90 and later program Knuth_Shuffle implicit none integer, parameter :: reps = 1000000 integer :: i, n integer, dimension(10) :: a, bins = 0, initial = (/ (n, n=1,10) /) do i = 1, reps a = initial call Shuffle(a) where (a == initial) bins = bins + 1 ! skew tester end do write(*, "(10(i8))") bins ! prints 100382 100007 99783 100231 100507 99921 99941 100270 100290 100442 contains subroutine Shuffle(a) integer, intent(inout) :: a(:) integer :: i, randpos, temp real :: r do i = size(a), 2, -1 call random_number(r) randpos = int(r * i) + 1 temp = a(randpos) a(randpos) = a(i) a(i) = temp end do end subroutine Shuffle end program Knuth_Shuffle  ## FreeBASIC ' version 22-10-2016 ' compile with: fbc -s console ' for boundry checks on array's compile with: fbc -s console -exx ' sort from lower bound to the highter bound ' array's can have subscript range from -2147483648 to +2147483647 Sub knuth_down(a() As Long) Dim As Long lb = LBound(a) Dim As ULong n = UBound(a) - lb +1 Dim As ULong i, j Randomize Timer For i = n -1 To 1 Step -1 j =Fix(Rnd * (i +1)) ' 0 <= j <= i Swap a(lb + i), a(lb + j) Next End Sub Sub knuth_up(a() As Long) Dim As Long lb = LBound(a) Dim As ULong n = UBound(a) - lb +1 Dim As ULong i, j Randomize Timer For i = 0 To n -2 j = Fix(Rnd * (n - i) + i) ' 0 <= j < n-i, + i ==> i <= j < n Swap a(lb + i), a(lb + j) Next End Sub ' ------=< MAIN >=------ Dim As Long i Dim As Long array(1 To 52), array2(-7 To 7) For i = 1 To 52 : array(i) = i : Next Print "Starting array" For i = 1 To 52 Print Using " ###";array(i); Next : Print : Print knuth_down(array()) Print "After Knuth shuffle downwards" For i = 1 To 52 Print Using " ###";array(i); Next : Print : Print For i = LBound(array2) To UBound(array2) array2(i) = i - LBound(array2) + 1 Next Print "Starting array, first index <> 0 " For i = LBound(array2) To UBound(array2) Print Using " ##";array2(i); Next : Print : Print knuth_up(array2()) Print "After Knuth shuffle upwards" For i = LBound(array2) To UBound(array2) Print Using " ##";array2(i); Next : Print : Print ' empty keyboard buffer While InKey <> "" : Wend Print : Print "hit any key to end program" Sleep End  Output: Starting array 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 After Knuth shuffle downwards 2 17 46 4 40 36 51 24 19 29 13 9 8 16 44 43 47 34 14 52 39 35 23 31 48 42 7 12 21 33 18 32 22 49 38 6 27 1 41 5 20 15 37 3 28 30 26 45 50 25 10 11 Starting array, first index <> 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 After Knuth shuffle upwards 4 1 9 10 15 11 12 7 3 5 8 13 6 14 2 ## Frink The built-in method array.shuffle[] implements the Fisher-Yates-Knuth shuffle algorithm: a = [1,2,3] a.shuffle[] ## FunL def shuffle( a ) = res = array( a ) n = a.length() for i <- 0:n r = rnd( i:n ) res(i), res(r) = res(r), res(i) res.toList() ## FutureBasic include "NSLog.incl" void local fn KnuthShuffle( mutArr as CFMutableArrayRef ) NSUInteger i, j, count count = len(mutArr) for i = count-1 to 1 step -1 j = rnd(i+1)-1 MutableArrayExchangeObjects( mutArr, i, j ) next end fn randomize CFMutableArrayRef mutArr NSUInteger i mutArr = fn MutableArrayWithObjects( @0, @1, @2, @3, @4, @5, @6, @7, @8, @9, NULL ) NSLog( @"Before shuffle: %@", fn ArrayComponentsJoinedByString( mutArr, @"" ) ) for i = 1 to 100 fn KnuthShuffle( mutArr ) NSLog( @"%@", fn ArrayComponentsJoinedByString( mutArr, @"" ) ) next HandleEvents Output: Before shuffle: 0123456789 1274860395 2715638904 7182035964 1297658403 2916574083 9162507843 1875962034 8721965034 7968402351 9347510862  ## Gambas Public Sub Main() Dim iTotal As Integer = 40 Dim iCount, iRand1, iRand2 As Integer Dim iArray As New Integer[] For iCount = 0 To iTotal iArray.add(iCount) Next Print "Original = "; For iCount = 0 To iArray.Max If iCount = iArray.max Then Print iArray[iCount]; Else Print iArray[iCount] & ","; Next For iCount = iTotal DownTo 0 iRand1 = Rand(iTotal) iRand2 = Rand(iTotal) Swap iArray[iRand1], iArray[iRand2] Next Print gb.NewLine & "Shuffled = "; For iCount = 0 To iArray.Max If iCount = iArray.max Then Print iArray[iCount]; Else Print iArray[iCount] & ","; Next End  Output: Original = 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40 Shuffled = 8,23,12,31,4,38,39,40,37,34,14,0,21,22,3,10,27,26,17,15,6,7,19,2,24,35,25,16,18,36,1,13,32,33,20,5,9,11,29,28,30  ## GAP # Return the list L after applying Knuth shuffle. GAP also has the function Shuffle, which does the same. ShuffleAlt := function(a) local i, j, n, t; n := Length(a); for i in [n, n - 1 .. 2] do j := Random(1, i); t := a[i]; a[i] := a[j]; a[j] := t; od; return a; end; # Return a "Permutation" object (a permutation of 1 .. n). # They are printed in GAP, in cycle decomposition form. PermShuffle := n -> PermList(ShuffleAlt([1 .. n])); ShuffleAlt([1 .. 10]); # [ 4, 7, 1, 5, 8, 2, 6, 9, 10, 3 ] PermShuffle(10); # (1,9)(2,3,6,4,5,10,8,7) # One may also call the built-in random generator on the symmetric group : Random(SymmetricGroup(10)); (1,8,2,5,9,6)(3,4,10,7)  ## Go (Note, in addition to these examples, rand.Shuffle was added in Go1.10 implementing a Fisher–Yates shuffle.) package main import ( "fmt" "math/rand" "time" ) func main() { var a int for i := range a { a[i] = i } fmt.Println(a) rand.Seed(time.Now().UnixNano()) for i := len(a) - 1; i >= 1; i-- { j := rand.Intn(i + 1) a[i], a[j] = a[j], a[i] } fmt.Println(a) }  To shuffle any type: package main import ( "fmt" "math/rand" "time" ) // Generic Knuth Shuffle algorithm. In Go, this is done with interface // types. The parameter s of function shuffle is an interface type. // Any type satisfying the interface "shuffler" can be shuffled with // this function. Since the shuffle function uses the random number // generator, it's nice to seed the generator at program load time. func init() { rand.Seed(time.Now().UnixNano()) } func shuffle(s shuffler) { for i := s.Len() - 1; i >= 1; i-- { j := rand.Intn(i + 1) s.Swap(i, j) } } // Conceptually, a shuffler is an indexed collection of things. // It requires just two simple methods. type shuffler interface { Len() int // number of things in the collection Swap(i, j int) // swap the two things indexed by i and j } // ints is an example of a concrete type implementing the shuffler // interface. type ints []int func (s ints) Len() int { return len(s) } func (s ints) Swap(i, j int) { s[i], s[j] = s[j], s[i] } // Example program. Make an ints collection, fill with sequential numbers, // print, shuffle, print. func main() { a := make(ints, 20) for i := range a { a[i] = i } fmt.Println(a) shuffle(a) fmt.Println(a) }  Example output: (of either program) [0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19] [11 10 12 19 4 13 15 17 14 2 5 18 8 0 6 9 7 3 1 16]  ## Groovy Solution: def shuffle = { list -> if (list == null || list.empty) return list def r = new Random() def n = list.size() (n..1).each { i -> def j = r.nextInt(i) list[[i-1, j]] = list[[j, i-1]] } list }  Test: def list = [] + (0..20) println list println shuffle(list) println shuffle(list) println shuffle(list)  Output: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] [12, 16, 7, 13, 1, 9, 17, 20, 15, 3, 5, 6, 8, 0, 18, 10, 14, 4, 2, 11, 19] [17, 6, 10, 1, 18, 5, 7, 13, 2, 11, 16, 3, 14, 0, 4, 20, 19, 12, 8, 9, 15] [6, 20, 11, 4, 7, 12, 5, 14, 19, 18, 13, 15, 1, 2, 8, 16, 17, 10, 0, 9, 3] ## Haskell import System.Random (randomRIO) mkRands :: Int -> IO [Int] mkRands = mapM (randomRIO . (,) 0) . enumFromTo 1 . pred replaceAt :: Int -> a -> [a] -> [a] replaceAt i c l = let (a, b) = splitAt i l in a ++ c : drop 1 b swapElems :: (Int, Int) -> [a] -> [a] swapElems (i, j) xs | i == j = xs | otherwise = replaceAt j (xs !! i)$ replaceAt i (xs !! j) xs

knuthShuffle :: [a] -> IO [a]
knuthShuffle xs = (foldr swapElems xs . zip [1 ..]) <$> mkRands (length xs)  or, as an alternative to making two indexed references into the list with (!!): import System.Random (randomRIO) import Data.Bool (bool) knuthShuffle :: [a] -> IO [a] knuthShuffle xs = (foldr swapped xs . zip [1 ..]) <$> randoms (length xs)

swapped :: (Int, Int) -> [a] -> [a]
swapped (i, j) xs =
let go (a, b)
| a == b = xs
| otherwise =
let (m, n) = bool (b, a) (a, b) (b > a)
(l, hi:t) = splitAt m xs
(ys, lo:zs) = splitAt (pred (n - m)) t
in concat [l, lo : ys, hi : zs]
in bool xs (go (i, j)) $((&&) . (i <) <*> (j <))$ length xs

randoms :: Int -> IO [Int]
randoms x = mapM (randomRIO . (,) 0) [1 .. pred x]

main :: IO ()
main = knuthShuffle ['a' .. 'k'] >>= print


Examples of use of either of the two versions above:

*Main> knuthShuffle  ['a'..'k']
"bhjdgfciake"

*Main> knuthShuffle $map(ap (,)(+10)) [0..9] [(0,10),(8,18),(2,12),(3,13),(9,19),(4,14),(7,17),(1,11),(6,16),(5,15)] Function for showing intermediate results: knuthShuffleProcess :: (Show a) => [a] -> IO () knuthShuffleProcess = (mapM_ print. reverse =<<). ap (fmap. (. zip [1..]). scanr swapElems) (mkRands. length)  Output: Detailed example *Main> knuthShuffleProcess ['a'..'k'] "abcdefghijk" "abckefghijd" "jbckefghiad" "jbckeighfad" "jbckeihgfad" "jbhkeicgfad" "jbhiekcgfad" "jbeihkcgfad" "ibejhkcgfad" "iebjhkcgfad" "iebjhkcgfad" An imperative implementation using arrays and the ST monad: import Data.Array.ST import Data.STRef import Control.Monad import Control.Monad.ST import Control.Arrow import System.Random shuffle :: RandomGen g => [a] -> g -> ([a], g) shuffle list g = runST$ do
r <- newSTRef g
let rand range = liftM (randomR range) (readSTRef r) >>=
runKleisli (second (Kleisli $writeSTRef r) >>> arr fst) a <- newAry (1, len) list forM_ [len, len - 1 .. 2]$ \n -> do
k <- rand (1, n)
runKleisli (Kleisli (writeArray a n) *** Kleisli (writeArray a k))
liftM2 (,) (getElems a) (readSTRef r)
where len = length list
newAry :: (Int, Int) -> [a] -> ST s (STArray s Int a)
newAry = newListArray


## Icon and Unicon

The shuffle method used here can shuffle lists, record fields, and strings:

procedure main()
show(shuffle([3,1,4,1,5,9,2,6,3]))
show(shuffle("this is a string"))
end

procedure shuffle(A)
every A[i := *A to 1 by -1] :=: A[?i]
return A
end

procedure show(A)
every writes(!A," ")
write()
end

Output:
->ks
9 6 1 4 3 1 3 5 2
i n   t i s   r t g   h s a i s
->

Note that the gloriously succinct 'standard' Icon shuffle:

procedure shuffle(A)
every !A :=: ?A
end


is subtly biased.

## Inform 6

[ shuffle a n i j tmp;
for(i = n - 1: i > 0: i--)
{
j = random(i + 1) - 1;

tmp = a->j;
a->j = a->i;
a->i = tmp;
}
];

## J

KS=:{~ (2&{.@[ {(|.@[)]} ])/@(,~(,.?@>:))@i.@#


The input array is transformed to a rectangular array of indexes. By doing this all kinds of arrays can serve as input (see examples below). The process is imitated by using using a fold, swapping elements in a restricted part of this index-array in each fold step.

process                         J

fold swap transform array   <==>  f / g y


Example of a transformed input:

(,~(,.?@>:))@i.@# 1+i.6
0 0 0 0 0 0
1 1 0 0 0 0
2 0 0 0 0 0
3 2 0 0 0 0
4 3 0 0 0 0
5 0 0 0 0 0
0 1 2 3 4 5


The last row is the index-array that has to be shuffled. The other rows have valid indexes in the first two columns. The second column has a randomized value <= value first column.

The index-swapping is done by the part:

2&{.@[ {(|.@[)]} ]


Finally, the shuffled indexes select elements from the original array.

input { ~ shuffled indexes


Alternatively, instead of creating a rectangular array, the swapping indices and the original data can be individually boxed.

In other words, (,~ (,. ?@>:))@i.@# can be replaced with |.@; ;&~./@(,. ?@>:)@i.@#, and the swapping can be achieved using (<@C. >)/ instead of (2&{.@[ {(|.@[)]} ])/.

With this approach, the data structure with the swapping indices and the original data could look like this:

    (|.@; ;&~./@(,. ?@>:)@i.@#)'abcde'
+---+-+---+---+-+-----+
|4 2|3|2 1|1 0|0|abcde|
+---+-+---+---+-+-----+


Note that we have the original data here, instead of indices to select all of its items. Note also that we have only a single value in a box where an item is being "swapped" with itself (this is required by J's cycle operation (C.)).

The resulting definition looks like this:

KS=: [: > (<@C. >)/@(|.@; ;&~./@(,. ?@>:)@i.@#)


Note that here we did not wind up with a list of indices which we used to permute the original data set. That data set is permuted directly. However, it is in a box and we do have to remove it from that box.

Permuting the data directly, instead of permuting indices, has performance implications when the items being swapped are large, but see the note at the end of this entry for J for how you would do this operation in a "real" J program.

Examples:
]A=: 5+i.9
5 6 7 8 9 10 11 12 13

Shuffle:
KS A
13 10 7 5 11 9 8 6 12

Input
]M=: /:~(1 2 3,:2 3 4),(11 2 3,: 0 11 2),(1 1 1,:1 0),:1 1 1,:1 0 1
1  1 1
1  0 0

1  1 1
1  0 1

1  2 3
2  3 4

11  2 3
0 11 2

Shuffle
KS M
11  2 3
0 11 2

1  1 1
1  0 1

1  1 1
1  0 0

1  2 3
2  3 4

Input
]L=:'aA';'bbB';'cC%$';'dD@' +--+---+----+---+ |aA|bbB|cC%$|dD@|
+--+---+----+---+

Shuffle
KS L
+--+----+---+---+
|aA|cC%$|dD@|bbB| +--+----+---+---+  In J the shuffling of an arbitrary array can easily be implemented by the phrase ( ref http://www.jsoftware.com/jwiki/JPhrases/RandomNumbers ): ({~?~@#)  Applied on the former examples: ({~?~@#) A 8 7 13 6 10 11 5 9 12 ({~?~@#) M 1 1 1 1 0 1 1 2 3 2 3 4 11 2 3 0 11 2 1 1 1 1 0 0 ({~?~@#) L +----+---+--+---+ |cC%$|bbB|aA|dD@|
+----+---+--+---+


## Java

import java.util.Random;

public static final Random gen = new Random();

// version for array of ints
public static void shuffle (int[] array) {
int n = array.length;
while (n > 1) {
int k = gen.nextInt(n--); //decrements after using the value
int temp = array[n];
array[n] = array[k];
array[k] = temp;
}
}
// version for array of references
public static void shuffle (Object[] array) {
int n = array.length;
while (n > 1) {
int k = gen.nextInt(n--); //decrements after using the value
Object temp = array[n];
array[n] = array[k];
array[k] = temp;
}
}


## JavaScript

### ES5

function knuthShuffle(arr) {
var rand, temp, i;

for (i = arr.length - 1; i > 0; i -= 1) {
rand = Math.floor((i + 1) * Math.random());//get random between zero and i (inclusive)
temp = arr[rand];//swap i and the zero-indexed number
arr[rand] = arr[i];
arr[i] = temp;
}
return arr;
}

var res = {
'1,2,3': 0, '1,3,2': 0,
'2,1,3': 0, '2,3,1': 0,
'3,1,2': 0, '3,2,1': 0
};

for (var i = 0; i < 100000; i++) {
res[knuthShuffle([1,2,3]).join(',')] += 1;
}

for (var key in res) {
print(key + "\t" + res[key]);
}


Results in:

1,2,3   16619
1,3,2   16614
2,1,3   16752
2,3,1   16959
3,1,2   16460
3,2,1   16596

### ES6

#### Mutating in-place swap

(() => {

// knuthShuffle :: [a] -> [a]
const knuthShuffle = xs =>
enumFromTo(0, xs.length - 1)
.reduceRight((a, i) => {
const
iRand =  randomRInt(0, i),
tmp = a[iRand];
return iRand !== i ? (
a[iRand] = a[i],
a[i] = tmp,
a
) : a;
}, xs);

const test = () => knuthShuffle(
(alpha beta gamma delta epsilon zeta
eta theta iota kappa lambda mu)
.split(/\s+/)
);

// GENERIC FUNCTIONS ----------------------------------

// enumFromTo :: Int -> Int -> [Int]
const enumFromTo = (m, n) =>
n >= m ? (
iterateUntil(x => x >= n, x => 1 + x, m)
) : [];

// iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a]
const iterateUntil = (p, f, x) => {
let vs = [x],
h = x;
while (!p(h))(h = f(h), vs.push(h));
return vs;
};

// randomRInt :: Int -> Int -> Int
const randomRInt = (low, high) =>
low + Math.floor(
(Math.random() * ((high - low) + 1))
);

return test();
})();

Output:

e.g.

["iota", "epsilon", "kappa", "theta", "gamma", "delta",
"lambda", "eta", "zeta", "beta", "mu", "alpha"]


#### Non-mutating swap

(() => {

// knuthShuffle :: [a] -> [a]
const knuthShuffle = xs =>
enumFromTo(0, xs.length - 1)
.reduceRight((a, i) => {
const iRand = randomRInt(0, i);
return i !== iRand ? (
swapped(i, iRand, a)
) : a;
}, xs);

const test = () => knuthShuffle(
(alpha beta gamma delta epsilon zeta
eta theta iota kappa lambda mu)
.split(/\s+/)
);

// Non mutating version of swapped

// swapped :: Int -> Int -> [a] -> [a]
const swapped = (iFrom, iTo, xs) =>
xs.map(
(x, i) => iFrom !== i ? (
iTo !== i ? (
x
) : xs[iFrom]
) : xs[iTo]
);

// GENERIC FUNCTIONS ----------------------------------

// enumFromTo :: Int -> Int -> [Int]
const enumFromTo = (m, n) =>
n >= m ? (
iterateUntil(x => x >= n, x => 1 + x, m)
) : [];

// iterateUntil :: (a -> Bool) -> (a -> a) -> a -> [a]
const iterateUntil = (p, f, x) => {
let vs = [x],
h = x;
while (!p(h))(h = f(h), vs.push(h));
return vs;
};

// randomRInt :: Int -> Int -> Int
const randomRInt = (low, high) =>
low + Math.floor(
(Math.random() * ((high - low) + 1))
);

// zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
const zipWith = (f, xs, ys) =>
Array.from({
length: Math.min(xs.length, ys.length)
}, (_, i) => f(xs[i], ys[i], i));

// MAIN ---
return test();
})();

Output:

e.g.

["mu", "theta", "beta", "eta", "delta", "epsilon",
"kappa", "alpha", "gamma", "lambda", "zeta", "iota"]


## Joy

DEFINE knuth-shuffle ==
(* Take the size of the array (without destroying it) *)
dup dup size
(* Generate a list of as many random numbers *)
[rand] [rem] enconcat map
(* Zip the two lists *)
swap zip
(* Sort according to the new index number *)
[small] [] [uncons unswonsd [first >] split [swons] dip2]
[enconcat] binrec
(* Delete the new index number *)
[second] map.

Using knuth-shuffle (file shuffle.joy):

(* Sorted array of 21 integers *)
[ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20]
knuth-shuffle.

Command line:

joy shuffle.joy
Output:
usrlib  is loaded
[12 6 8 4 14 18 7 15 1 0 11 13 5 10 16 2 19 17 9 20 3]


## jq

Works with: jq

Works with gojq, the Go implementation of jq

Neither the C nor the Go implementations of jq has a built-in PRNG, but both are designed with the Unix toolset philosophy in mind, so in this entry we will use an external source of randomness rather than one of the PRNGs defined in jq as at RC.

Specifically, we will use /dev/urandom like so:

< /dev/urandom tr -cd '0-9' | fold -w 1 | jq -RMnrc -f program.jq

where program.jq is the following program:

# 52-card deck:
def deck:
[range(127137; 127148), range(127149; 127151),  # Spades
range(127153; 127164), range(127165; 127167),  # Hearts
range(127169; 127180), range(127181; 127183),  # Diamonds
range(127185; 127196), range(127197; 127199)]  # Clubs
;

# For splitting a deck into hands :-)
def nwise($n): def n: if length <=$n then . else .[0:$n] , (.[$n:] | n) end;
n;

# Output: a prn in range(0;$n) where$n is ., and $n > 0 def prn: if . == 1 then 0 else . as$n
| (($n-1)|tostring|length) as$w
| [limit($w; inputs)] | join("") | tonumber | if . <$n then . else ($n | prn) end end; def knuthShuffle: length as$n
| if $n <= 1 then . else {i:$n, a: .}
| until(.i ==  0;
.i += -1
| (.i + 1 | prn) as $j | .a[.i] as$t
| .a[.i] = .a[$j] | .a[$j] = $t) | .a end; def task: [], [10,20], [10,20,30] | knuthShuffle; task, (deck|knuthShuffle | nwise(13) | implode) Output: [] [10,20] [20,30,10]  🂶🃚🃈🃘🃊🂥🃉🂽🂣🂸🃂🂺🃗 🂵🃁🃇🂮🂹🃝🃆🂱🂻🂩🃋🂭🃖 🂢🃛🃕🃃🂾🃙🃞🂨🂪🂲🂷🃍🂫 🂦🃒🃔🂳🂡🃓🃄🂴🃅🃎🃑🂤🂧 ## Julia Works with: Julia version 0.6 function knuthshuffle!(r::AbstractRNG, v::AbstractVector) for i in length(v):-1:2 j = rand(r, 1:i) v[i], v[j] = v[j], v[i] end return v end knuthshuffle!(v::AbstractVector) = knuthshuffle!(Base.Random.GLOBAL_RNG, v) v = collect(1:20) println("# v =$v\n   -> ", knuthshuffle!(v))

Output:
# v = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
-> [16, 5, 17, 10, 2, 7, 20, 14, 4, 8, 19, 15, 18, 12, 11, 1, 9, 13, 3, 6]

## Kotlin

object Knuth {
internal val gen = java.util.Random()
}

fun <T> Array<T>.shuffle(): Array<T> {
val a = clone()
var n = a.size
while (n > 1) {
val k = Knuth.gen.nextInt(n--)
val t = a[n]
a[n] = a[k]
a[k] = t
}
return a
}

fun main(args: Array<String>) {
val str = "abcdefghijklmnopqrstuvwxyz".toCharArray()
(1..10).forEach {
val s = str.toTypedArray().shuffle().toCharArray()
println(s)
require(s.toSortedSet() == str.toSortedSet())
}

val ia = arrayOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
(1..10).forEach {
val s = ia.shuffle()
println(s.distinct())
require(s.toSortedSet() == ia.toSet())
}
}

Output:
xdhsvtnumjgbywiqoapcelkrfz
pjnegbiyzuhsrclodftwkmaqvx
bkmqwhzregifyanvsltxjupodc
ewhxrlybnjqpvdsozaimkucgft
pdqgoaymbzefnjrwuvilsckxht
kcpagyuehjswdtvnzfrlbxqomi
iztsmaygkblephcjfnwvxurdoq
pltdyjwivsehckzfaxruqogmbn
nytfbpmjicgkaueoxwrhlsqvdz
epucijbvrhwyzdlsqftagxmkon
[7, 4, 5, 9, 2, 1, 3, 8, 10, 6]
[8, 10, 5, 4, 3, 6, 1, 2, 7, 9]
[7, 9, 2, 1, 10, 4, 6, 5, 8, 3]
[9, 6, 1, 8, 2, 5, 10, 3, 4, 7]
[7, 3, 6, 9, 10, 2, 5, 4, 1, 8]
[2, 9, 1, 7, 5, 10, 8, 4, 6, 3]
[4, 2, 7, 3, 8, 5, 6, 10, 1, 9]
[4, 8, 7, 6, 10, 5, 2, 1, 3, 9]
[6, 3, 9, 4, 5, 2, 10, 8, 1, 7]
[3, 6, 9, 2, 10, 8, 7, 5, 1, 4]

## LabVIEW

Works with: LabVIEW version 8.0 Full Development System

## Lambdatalk

{def shuffle

{def shuffle.in
{lambda {:a}
{S.map {{lambda {:a :i}
{A.swap :i
{floor {* {random} {+ :i 1}}}  // j = random integer from 0 to i+1
:a}} :a}
{S.serie {- {A.length :a} 1} 0 -1}}}}           // from length-1 to 0

{lambda {:a}
{let { {:b {A.duplicate :a}} }        // optionnaly prevents modifying the original array
{S.replace \s by in {shuffle.in :b}  // trim extra spaces
:b}}}}                              // return the new array
-> shuffle

{def A.swap                                    // should probably be promoted as a primitive
{lambda {:i :j :a}
{let { {:i :i}
{:gja {A.get :j :a}}
{:b {A.set! :j {A.get :i :a} :a}}
} {let { {_ {A.set! :i :gja :b} }}}}}}  // side effect without any return value
-> A.swap

{def B {A.new a b c d e f g h i j k l m n o p q r s t u v w x y z}}
-> B

{shuffle {B}}
-> [z,t,q,w,c,n,a,u,r,y,i,s,f,d,g,m,h,x,b,e,k,p,l,o,j,v]


## Lasso

define staticarray->swap(p1::integer,p2::integer) => {
fail_if(
#p1 < 1 or #p2 < 1 or
#p1 > .size or #p2 > .size,
'invalid parameters'
)
#p1 == #p2
? return

local(tmp) = .get(#p2)
.get(#p2)  = .get(#p1)
.get(#p1)  = #tmp
}
define staticarray->knuthShuffle => {
loop(-from=.size, -to=2, -by=-1) => {
.swap(math_random(1, loop_count), loop_count)
}
}

(1 to 10)->asStaticArray->knuthShuffle&asString

Output:
staticarray(9, 5, 6, 1, 10, 8, 3, 4, 2, 7)

## Liberty BASIC

'Declared the UpperBound to prevent confusion with lots of 9's floating around....
UpperBound = 9
Dim array(UpperBound)

For i = 0 To UpperBound
array(i) = Int(Rnd(1) * 10)
Print array(i)
Next i

For i = 0 To UpperBound
'set a random value because we will need to use the same value twice
randval = Int(Rnd(1) * (UpperBound - i))
temp1 = array(randval)
temp2 = array((UpperBound - i))
array(randval) = temp2
array((UpperBound - i)) = temp1
Next i

Print
For i = 0 To UpperBound
Print array(i)
Next i

## Logo

to swap :i :j :a
localmake "t item :i :a
setitem :i :a item :j :a
setitem :j :a :t
end
to shuffle :a
for [i [count :a] 2] [swap 1 + random :i :i :a]
end

make "a {1 2 3 4 5 6 7 8 9 10}
shuffle :a
show :a

Lhogho does not have a setitem, and also does things more 'function'ally.

to slice :lst :start :finish
local "res
make "res []
for "i [:start :finish 1] [
make "j item :i :lst
make "res se :res :j
]
op :res
end

to setitem :n :lst :val
local "lhs
local "rhs
make "lhs slice :lst 1 :n-1
make "rhs slice :lst :n+1 count :lst
op (se :lhs :val :rhs)
end

to swap :i :j :a
local "t
make "t item :i :a
make "a setitem :i :a item :j :a
make "a setitem :j :a :t
op :a
end

to shuffle :a
for "i [count :a 2]
[
make "a swap 1 + random :i :i :a
]
op :a
end

make "a ( list 1 2 3 4 5 6 7 8 9 10 )
make "a shuffle :a
show :a

## Lua

function table.shuffle(t)
for n = #t, 1, -1 do
local k = math.random(n)
t[n], t[k] = t[k], t[n]
end

return t
end

math.randomseed( os.time() )
a = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
table.shuffle(a)
for i,v in ipairs(a) do print(i,v) end


## M2000 Interpreter

Dim Base 0, A(3)
For k=1 to 6 {
A(0):=10,20, 30
For i=len(A())-1 to 0 {
let j=random(0,i)
Swap a(i), a(j)
}
Print A()
}

## M4

divert(-1)
define(randSeed',141592653)
define(rand_t',eval(randSeed^(randSeed>>13))')
define(random',
define(randSeed',eval((rand_t^(rand_t<<18))&0x7fffffff))randSeed')
define(for',
ifelse($#,0,$0'',
ifelse(eval($2<=$3),1,
pushdef($1',$2)$4'popdef($1')$0($1',incr($2),$3,$4')')')') define(set',define($1[$2]',$3')')
define(get',defn($1[$2])')
define(new',set($1,size,0)') define(deck', new($1)for(x',1,$2, set($1',x,x)')'set($1',size,$2)')
define(show',
for(x',1,get($1,size),get($1,x)'ifelse(x,get($1,size),',, ')')') define(swap',set($1,$2,get($1,$4))'set($1,$4,$3)')
define(shuffle',
define(s',get($1,size))'for(x',1,decr(s), swap($1,x,get($1,x),eval(x+random%(s-x+1)))')') divert deck(b',52) show(b') shuffle(b') show(b') Output: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52 6, 22, 33, 51, 35, 45, 16, 32, 7, 34, 10, 44, 5, 38, 43, 25, 29, 9, 37, 20, 21, 48, 24, 46, 8, 26, 41, 47, 49, 36, 14, 31, 15, 39, 12, 17, 13, 1, 3, 4, 27, 11, 28, 2, 19, 30, 42, 50, 18, 52, 40, 23  ## Mathematica/Wolfram Language Usage of built-in function: RandomSample[{1, 2, 3, 4, 5, 6}]  Custom function: Shuffle[input_List /; Length[input] >= 1] := Module[{indices = {}, allindices = Range[Length[input]]}, Do[ AppendTo[indices, Complement[allindices, indices][[RandomInteger[{1, i}]]]]; , {i, Length[input], 1, -1} ]; input[[indices]] ]  Example: Shuffle[{1, 2, 3, 4, 5, 6}]  ## MATLAB Because this shuffle is done using rounds of operations on subsets of decreasing size, this is not an algorithm that can be vectorized using built-in MATLAB functions. So, we have to go old-school, no fancy MATLAB trickery. function list = knuthShuffle(list) for i = (numel(list):-1:2) j = floor(i*rand(1) + 1); %Generate random int between 1 and i %Swap element i with element j. list([j i]) = list([i j]); end end  There is an alternate way to do this that is not a true Knuth Shuffle, but operates with the same spirit. This alternate version produces the same output, saves some space, and can be implemented in-line without the need to encapsulate it in a function call like the Knuth Shuffle. function list = randSort(list) list = list( randperm(numel(list)) ); end  ## Maxima /* Maxima has an implementation of Knuth shuffle */ random_permutation([a, b, c]);  ## Modula-3 MODULE Shuffle EXPORTS Main; IMPORT IO, Fmt, Random; VAR a := ARRAY [0..9] OF INTEGER {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; PROCEDURE Shuffle(VAR a: ARRAY OF INTEGER) = VAR temp: INTEGER; n: INTEGER := NUMBER(a); BEGIN WITH rand = NEW(Random.Default).init() DO WHILE n > 1 DO WITH k = rand.integer(0, n - 1) DO DEC(n); temp := a[n]; a[n] := a[k]; a[k] := temp; END; END; END; END Shuffle; BEGIN Shuffle(a); FOR i := FIRST(a) TO LAST(a) DO IO.Put(Fmt.Int(a[i]) & " "); END; IO.Put("\n"); END Shuffle.  Output: martin@thinkpad:~$ ./shuffle
9 2 7 3 6 8 4 5 1 10
martin@thinkpad:~$./shuffle 1 7 8 10 5 4 6 3 9 2  ## MUMPS Shuffle(items,separator) New ii,item,list,n Set list="",n=0 Set ii="" For Set ii=$Order(items(ii)) Quit:ii=""  Do
. Set n=n+1,list(n)=items(ii),list=list_$Char(n) . Quit For Quit:list="" Do . Set n=$Random($Length(list))+1 . Set item=list($ASCII(list,n))
. Set $Extract(list,n)="" . Write item,separator . Quit Quit CardDeck New card,ii,suite Set ii=0 For suite="Spades","Hearts","Clubs","Diamonds" Do . For card=2:1:10,"Jack","Queen","King","Ace" Do . . Set ii=ii+1,items(ii)=card_" of "_suite . . Quit . Quit Quit Kill items Set items(91)="Red" Set items(82)="White" Set items(73)="Blue" Set items(64)="Yellow" Set items(55)="Green" Do Shuffle(.items," ") ; Red Yellow White Green Blue Do Shuffle(.items," ") ; Red Blue Yellow White Green Do Shuffle(.items," ") ; Green Blue Yellow White Red Kill items Do CardDeck,Shuffle(.items,$Char(13,10))
Queen of Hearts
9 of Diamonds
10 of Hearts
King of Hearts
7 of Diamonds
9 of Clubs
6 of Diamonds
8 of Diamonds
Ace of Hearts
Queen of Diamonds
9 of Hearts
2 of Hearts
King of Clubs
7 of Clubs
6 of Clubs
3 of Diamonds
Queen of Clubs
4 of Hearts
Ace of Diamonds
Ace of Clubs
10 of Diamonds
Jack of Diamonds
8 of Clubs
Jack of Hearts
10 of Clubs
4 of Diamonds
3 of Hearts
2 of Diamonds
5 of Hearts
Jack of Clubs
2 of Clubs
5 of Diamonds
6 of Hearts
4 of Clubs
3 of Clubs
7 of Hearts
8 of Hearts
King of Diamonds
5 of Clubs

## Nemerle

Shuffle[T] (arr : array[T]) : array[T]
{
def rnd = Random();

foreach (i in [0 .. (arr.Length - 2)])
arr[i] <-> arr[(rnd.Next(i, arr.Length))];
arr
}


## NetRexx

### version 1

/* NetRexx */
options replace format comments java crossref savelog symbols nobinary

import java.util.List

cards = [String -
'hA', 'h2', 'h3', 'h4', 'h5', 'h6', 'h7', 'h8', 'h9', 'h10', 'hJ', 'hQ', 'hK' -
, 'cA', 'c2', 'c3', 'c4', 'c5', 'c6', 'c7', 'c8', 'c9', 'c10', 'cJ', 'cQ', 'cK' -
, 'dA', 'd2', 'd3', 'd4', 'd5', 'd6', 'd7', 'd8', 'd9', 'd10', 'dJ', 'dQ', 'dK' -
, 'sA', 's2', 's3', 's4', 's5', 's6', 's7', 's8', 's9', 's10', 'sJ', 'sQ', 'sK' -
]
cardsLen = cards.length
deck = ArrayList(cardsLen)
loop c_ = 0 to cardsLen - 1
end c_

showHand(deck)
deck = ArrayList shuffle(deck)
showHand(deck)

return

method shuffle(deck = List) public static binary returns List

rn = Random()
dl = deck.size

loop i_ = dl - 1 to 1 by -1
j_ = rn.nextInt(i_)
__ = deck.get(i_)
deck.set(i_, deck.get(j_))
deck.set(j_, __)
end i_

return deck

method showHand(deck = ArrayList) public static binary

dl = deck.size
hl = dl % 4
loop c_ = 0 to dl - 1 by hl
d_ = c_ + hl
if d_ >= dl then d_ = dl
say ArrayList(deck.subList(c_, d_)).toString
end c_
say

return

Output:
[hA, h2, h3, h4, h5, h6, h7, h8, h9, h10, hJ, hQ, hK]
[cA, c2, c3, c4, c5, c6, c7, c8, c9, c10, cJ, cQ, cK]
[dA, d2, d3, d4, d5, d6, d7, d8, d9, d10, dJ, dQ, dK]
[sA, s2, s3, s4, s5, s6, s7, s8, s9, s10, sJ, sQ, sK]

[s8, c10, sJ, c8, h10, h3, s3, d6, hJ, d3, c7, h5, s5]
[h8, d10, cK, s6, dQ, d9, d4, c4, c6, h6, cA, sA, dK]
[dJ, dA, d7, c2, d2, s10, sK, h2, c5, s7, cJ, d5, h9]
[c9, d8, c3, s9, cQ, sQ, h4, s4, hQ, h7, hK, hA, s2]


### version 2

/* NetRexx ------------------------------------------------------------
* 08.01.2014 Walter Pachl modified to show state development a la Rexx
*--------------------------------------------------------------------*/
options replace format comments java crossref savelog symbols nobinary

import java.util.List

cards = [String '1','2','3','4','5','6','7','8','9','10']
cardsLen = cards.length
deck = ArrayList(cardsLen)
loop c_ = 0 to cardsLen - 1
end c_

showHand(deck,'In ')
deck = ArrayList shuffle(deck)
showHand(deck,'Out')
return

method shuffle(deck = List) public static binary returns List
rn = Random()
dl = deck.size
loop i_ = dl - 1 to 1 by -1
j_ = rn.nextInt(i_)
__ = deck.get(i_)
deck.set(i_, deck.get(j_))
deck.set(j_, __)
say i_ j_ ArrayList(deck.subList(0,i_+1)).toString
end i_
return deck

method showHand(deck = ArrayList,tag=REXX) public static binary
say tag ArrayList(deck.subList(0,deck.size)).toString
return

Output:
In  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
9 5 [1, 2, 3, 4, 5, 10, 7, 8, 9, 6]
8 4 [1, 2, 3, 4, 9, 10, 7, 8, 5]
7 2 [1, 2, 8, 4, 9, 10, 7, 3]
6 0 [7, 2, 8, 4, 9, 10, 1]
5 4 [7, 2, 8, 4, 10, 9]
4 1 [7, 10, 8, 4, 2]
3 2 [7, 10, 4, 8]
2 0 [4, 10, 7]
1 0 [10, 4]
Out [10, 4, 7, 8, 2, 9, 1, 3, 5, 6]

## Nim

Note that the function "shuffle" exists in the standard module "random" and that it uses the Knuth shuffle.

import random
randomize()

proc shuffle[T](x: var openArray[T]) =
for i in countdown(x.high, 1):
let j = rand(i)
swap(x[i], x[j])

var x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
shuffle(x)
echo x


## Objective-C

#import <Foundation/Foundation.h>

@interface NSMutableArray (KnuthShuffle)
- (void)knuthShuffle;
@end
@implementation NSMutableArray (KnuthShuffle)
- (void)knuthShuffle {
for (NSUInteger i = self.count-1; i > 0; i--) {
NSUInteger j = arc4random_uniform(i+1);
[self exchangeObjectAtIndex:i withObjectAtIndex:j];
}
}
@end

int main() {
@autoreleasepool {
NSMutableArray *x = [NSMutableArray arrayWithObjects:@0, @1, @2, @3, @4, @5, @6, @7, @8, @9, nil];
[x knuthShuffle];
NSLog(@"%@", x);
}
return 0;
}

Output:
(
9,
4,
0,
8,
5,
3,
2,
1,
7,
6
)


## OCaml

let shuffle arr =
for n = Array.length arr - 1 downto 1 do
let k = Random.int (n + 1) in
let temp = arr.(n) in
arr.(n) <- arr.(k);
arr.(k) <- temp
done


## Oforth

Works with any object that has the property to be Indexable (Lists, Intervals, ...) Returns a new list

Indexable method: shuffle
| s i l |
self asListBuffer ->l
self size dup ->s 1- loop: i [ s i - rand i +  i  l swapValues ]
l dup freeze ;

## Ol

There are two functions - one for tuples (that speedy) and second for lists (that uses previous one).

Ol is functional language, so we should make a copy of shuffling tuple and return this shuffled copy.

(define (shuffle tp)
(let ((items (vm:cast tp (type tp)))) ; make a copy
(for-each (lambda (i)
(let ((a (ref items i))
(j (+ 1 (rand! i))))
(set-ref! items i (ref items j))
(set-ref! items j a)))
(reverse (iota (size items) 1)))
items))

(define (list-shuffle tp)
(map (lambda (i)
(list-ref tp i))
(tuple->list
(shuffle (list->tuple (iota (length tp)))))))


Testing:

(define items (tuple 1 2 3 4 5 6 7 8 9))
(print "tuple before: " items)
(print "tuple after: " (shuffle items))

(define items (list 1 2 3 4 5 6 7 8 9))
(print "list before: " items)
(print "list after: " (list-shuffle items))


Output:

tuple before: #[1 2 3 4 5 6 7 8 9]
tuple after: #[9 4 1 3 7 2 5 6 8]
list before: (1 2 3 4 5 6 7 8 9)
list after: (8 2 4 9 5 3 6 1 7)


## Oz

declare
proc {Shuffle Arr}
Low = {Array.low Arr}
High = {Array.high Arr}
in
for I in High..Low;~1 do
J = Low + {OS.rand} mod (I - Low + 1)
OldI = Arr.I
in
Arr.I := Arr.J
Arr.J := OldI
end
end

X = {Tuple.toArray unit(0 1 2 3 4 5 6 7 8 9)}
in
{Show {Array.toRecord unit X}}
{Shuffle X}
{Show {Array.toRecord unit X}}

## PARI/GP

FY(v)={
forstep(n=#v,2,-1,
my(i=random(n)+1,t=v[i]);
v[i]=v[n];
v[n]=t
);
v
};

FY(vector(52,i,i))

## Pascal

program Knuth;

const
startIdx = -5;
max = 11;
type
tmyData = string;
tmylist = array [startIdx..startIdx+max-1] of tmyData;

procedure InitList(var a: tmylist);
var
i: integer;
Begin
for i := Low(a) to High(a) do
str(i:3,a[i])
end;

procedure shuffleList(var a: tmylist);
var
i,k : integer;
tmp: tmyData;
begin
for i := High(a)-low(a) downto 1 do begin
k := random(i+1) + low(a);
tmp := a[i+low(a)]; a[i+low(a)] := a[k]; a[k] := tmp
end
end;

procedure DisplayList(const a: tmylist);
var
i : integer;
Begin
for i := Low(a) to High(a) do
write(a[i]);
writeln
end;

{ Test and display }
var
a: tmylist;
i: integer;
begin
randomize;
InitList(a);
DisplayList(a);
writeln;
For i := 0 to 4 do
Begin
shuffleList(a);
DisplayList(a);
end;
end.

Output:
 -5 -4 -3 -2 -1  0  1  2  3  4  5

-5  4  0 -4  3 -1 -3  1 -2  5  2
2  0  1 -5 -1  5 -3  4 -2  3 -4
3 -1 -2  5 -4  1  2 -5 -3  4  0
-4  1 -1 -5  5  2  0  3 -2 -3  4
-3 -5  4  2 -4  0  5  3  1 -1 -2

## Perl

sub shuffle {
my @a = @_;
foreach my $n (1 ..$#a) {
my $k = int rand$n + 1;
$k ==$n or @a[$k,$n] = @a[$n,$k];
}
return @a;
}


## Phix

sequence cards = tagset(52)
puts(1,"Before: ")      ?cards
for i=52 to 1 by -1 do
integer r = rand(i)
{cards[r],cards[i]} = {cards[i],cards[r]}
end for
puts(1,"After:  ")      ?cards
puts(1,"Sorted: ")      ?sort(cards)

Output:
Before: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52}
After:  {42,4,48,28,11,3,52,51,22,2,49,38,25,33,27,35,18,44,5,7,21,13,36,29,43,6,9,31,10,30,20,16,46,34,8,17,14,45,37,24,32,41,50,15,39,40,47,23,1,12,26,19}
Sorted: {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52}


## PHP

//The Fisher-Yates original Method
function yates_shuffle($arr){$shuffled = Array();
while($arr){$rnd = array_rand($arr);$shuffled[] = $arr[$rnd];
array_splice($arr,$rnd, 1);
}
return $shuffled; } //The modern Durstenfeld-Knuth algorithm function knuth_shuffle(&$arr){
for($i=count($arr)-1;$i>0;$i--){
$rnd = mt_rand(0,$i);
list($arr[$i], $arr[$rnd]) = array($arr[$rnd], $arr[$i]);
}
}


## Picat

go =>
_ = random2(),
L = 1..10,
println(l_before=L),
knuth_shuffle(L),
println('l_after '=L),
nl.

knuth_shuffle(L) =>
foreach(I in L.len..-1..1)
J = random(1,I),
Tmp = L[I],
L[I] := L[J],
L[J] := Tmp
end.
Output:
l_before = [1,2,3,4,5,6,7,8,9,10]
l_after  = [2,9,6,7,10,3,5,4,8,1]

## PicoLisp

(seed (in "/dev/urandom" (rd 8)))

(de knuth (Lst)
(for (N (length Lst) (>= N 2) (dec N))
(let I (rand 1 N)
(xchg (nth Lst N) (nth Lst I)) ) ) )

(let L (range 1 15)
(println 'before L)
(knuth L)
(println 'after L) )
Output:
before (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15)
after (12 15 4 13 11 9 7 1 2 14 5 6 8 3 10)


## PL/I

### version 1

declare T(0:10) fixed binary initial (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
declare (i, j, temp) fixed binary;
do i = lbound(T,1) to hbound(T,1);
j = min(random() * 12, 11);
temp = T(j);   T(j) = T(i);   T(i) = temp;
end;

### version 2

 kn: Proc Options(main);
/*--------------------------------------------------------------------
* 07.01.2014 Walter Pachl  translated from REXX version 2
* Iteration i: only the first i elements are candidates for swapping
*-------------------------------------------------------------------*/
Dcl T(10) Bin Fixed(15) Init(1,2,3,4,5,6,7,8,9,10);
Dcl (i,j,temp) Bin Fixed(15) init(0);
Dcl h Char(6);
Call show('In',10);                   /* show start                 */
do i = 10 To 2 By -1;                 /* shuffle                    */
j=random()*i+1;
Put string(h)Edit(i,j)(f(2),f(3));
temp=t(i); t(i)=t(j); t(j)=temp;    /* t(i) <-> t(j)              */
Call show(h,i);                     /* show intermediate states   */
end;
Call show('Out',10);                  /* show final state           */

show: Proc(txt,n);
Dcl txt Char(*);
Dcl n   Bin Fixed(15);
Put Edit(txt,(t(k) do k=1 To n))(Skip,a(7),10(f(3)));
End;
end;
Output:
In       1  2  3  4  5  6  7  8  9 10
10  5    1  2  3  4 10  6  7  8  9  5
9  1    9  2  3  4 10  6  7  8  1
8  7    9  2  3  4 10  6  8  7
7  2    9  8  3  4 10  6  2
6  6    9  8  3  4 10  6
5  3    9  8 10  4  3
4  2    9  4 10  8
3  3    9  4 10
2  1    4  9
Out      4  9 10  8  3  6  2  7  1  5

## PowerShell

Works with: PowerShell version 3
$A = 1, 2, 3, 4, 5 Get-Random$A -Count $A.Count  Works with: PowerShell version 2 function shuffle ($a) {
$c =$a.Clone()  # make copy to avoid clobbering $a 1..($c.Length - 1) | ForEach-Object {
$i = Get-Random -Minimum$_ -Maximum $c.Length$c[$_-1],$c[$i] =$c[$i],$c[$_-1]$c[$_-1] # return newly-shuffled value }$c[-1]  # last value
}


This yields the values one by one instead of returning the array as a whole, so the rest of the pipeline can work on the values while shuffling is still in progress.

## PureBasic

EnableExplicit

Procedure KnuthShuffle(Array a(1))
Protected i, last = ArraySize(a())

For i = last To 1 Step -1
Swap a(i), a(Random(i))
Next
EndProcedure

Procedure.s ArrayToString(Array a(1))
Protected ret$, i, last = ArraySize(a()) ret$ = Str(a(0))
For i = 1 To last
ret$+ "," + Str(a(i)) Next ProcedureReturn ret$
EndProcedure

#NumElements = 10

Dim a(#NumElements-1)
Define i

For i = 0 To #NumElements-1
a(i) = i
Next

KnuthShuffle(a())
Debug "shuffled: " + ArrayToString(a())

Output:
shuffled: 1,8,6,0,5,9,2,4,7,3

## Python

Python's standard library function random.shuffle uses this algorithm and so should normally be used. The function below is very similar:

from random import randrange

def knuth_shuffle(x):
for i in range(len(x)-1, 0, -1):
j = randrange(i + 1)
x[i], x[j] = x[j], x[i]

x = list(range(10))
knuth_shuffle(x)
print("shuffled:", x)

Output:
shuffled: [5, 1, 6, 0, 8, 4, 2, 3, 9, 7]


We could also write our own Knuth shuffle function as a fold, with a non-mutating swap function:

Works with: Python version 3.7
'''Knuth shuffle as a fold'''

from functools import reduce
from random import randint

# knuthShuffle :: [a] -> IO [a]
def knuthShuffle(xs):
'''A pseudo-random shuffle of the elements in xs.'''
return reduce(
swapped,
enumerate(randoms(len(xs))), xs
)

# swapped :: (Int, Int) -> [a] -> [a]
def swapped(xs, ij):
'''New list in which the elements at indices
i and j of xs are swapped.
'''
def go(a, b):
if a != b:
m, n = (a, b) if b > a else (b, a)
l, ht = splitAt(m)(xs)
ys, zs = splitAt((n - m) - 1)(ht[1:])
return l + [zs] + ys + [ht] + zs[1:]
else:
return xs
i, j = ij
z = len(xs) - 1
return xs if i > z or j > z else go(i, j)

# randoms :: Int -> IO [Int]
def randoms(n):
'''Pseudo-random list of n - 1 indices.
'''
return list(map(randomRInt(0)(n - 1), range(1, n)))

# TEST ----------------------------------------------------
# main :: IO ()
def main():
'''Repeated Knuth shuffles of ['a' .. 'k']'''

print(
fTable(main.__doc__ + ':\n')(str)(lambda x: ''.join(x))(
lambda _: knuthShuffle(list('abcdefghijk'))
)(range(1, 11))
)

# GENERIC -------------------------------------------------

# randomRInt :: Int -> Int -> IO () -> Int
def randomRInt(m):
'''The return value of randomRInt is itself
a function. The returned function, whenever
called, yields a a new pseudo-random integer
in the range [m..n].
'''
return lambda n: lambda _: randint(m, n)

# splitAt :: Int -> [a] -> ([a], [a])
def splitAt(n):
'''A tuple pairing the prefix of length n
with the rest of xs.
'''
return lambda xs: (xs[0:n], xs[n:])

# FORMATTING -----------------------------------------------------------

# fTable :: String -> (a -> String) ->
#                     (b -> String) -> (a -> b) -> [a] -> String
def fTable(s):
'''Heading -> x display function -> fx display function ->
f -> xs -> tabular string.
'''
def go(xShow, fxShow, f, xs):
ys = [xShow(x) for x in xs]
w = max(map(len, ys))
return s + '\n' + '\n'.join(map(
lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)),
xs, ys
))
return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
xShow, fxShow, f, xs
)

# MAIN ---
if __name__ == '__main__':
main()

Output:
Repeated Knuth shuffles of ['a' .. 'k']:

1 -> kdafbhigejc
2 -> jhdkgeicabf
3 -> aciebghdfkj
4 -> fjahegibckd
5 -> cabejfidkgh
6 -> gbecahfkijd
7 -> jegchkdifba
9 -> ihfebdajgkc
10 -> hjkigbadcfe

## Quackery

The word shuffle is predefined in Quackery (and shown below) - it shuffles a nest (an immutable dynamic array) by removing random items from the nest (i.e. creating a new array with that item removed) and appending them to an (initially empty) nest (i.e. creating a new array with that item appended). It fits the criteria for this task with the relaxations noted at the end of the task description.

The word knuffle is probably an entirely in-place shuffle, if the dynamic memory allocation routines for a particular implementation of Quackery allow in-place modification of a dynamic array when there is only a single pointer to the array. (After the first invocation of poke inside [exch] there will definitely only be a single pointer to the array.)

  [ [] swap dup size times
[ dup size random pluck
nested rot join swap ]
drop ]                      is shuffle (     [ --> [ )

[ temp put
2dup swap
temp share swap peek
temp share rot peek
dip
[ swap
temp take
swap poke
temp put ]
swap
temp take
swap poke ]                 is [exch]  ( n n [ --> [ )

[ dup size 1 - times
[ i 1+ dup 1+ random
rot [exch] ] ]         is knuffle (     [ --> [ )
Output:

Testing in the Quackery shell (REPL).

/O> ' [ 10 11 12 13 14 15 16 17 18 19 ]
... 10 times [ knuffle dup echo cr ]
...
[ 14 19 11 13 18 17 10 16 12 15 ]
[ 10 15 18 17 13 14 12 16 11 19 ]
[ 19 11 10 14 15 16 12 18 17 13 ]
[ 14 13 19 15 10 16 11 17 18 12 ]
[ 18 13 11 15 17 16 12 10 14 19 ]
[ 18 17 10 13 12 19 15 16 14 11 ]
[ 10 19 17 12 13 14 15 16 18 11 ]
[ 10 16 17 18 13 11 15 19 12 14 ]
[ 18 19 17 11 10 14 16 12 13 15 ]
[ 19 11 10 14 16 12 17 18 15 13 ]

Stack: [ 10 15 13 14 12 19 16 11 17 18 ]

/O> 10 times [ shuffle dup echo cr ]
...
[ 10 13 11 14 18 15 12 17 16 19 ]
[ 12 19 16 17 10 13 14 11 18 15 ]
[ 11 14 12 17 15 19 13 16 18 10 ]
[ 17 15 14 18 16 19 11 10 13 12 ]
[ 14 15 18 13 10 16 17 12 19 11 ]
[ 12 14 11 16 15 10 19 18 17 13 ]
[ 14 12 15 18 16 19 11 10 13 17 ]
[ 18 19 15 16 14 12 13 11 17 10 ]
[ 14 18 19 11 16 12 13 15 17 10 ]
[ 17 19 11 18 14 10 12 13 16 15 ]

Stack: [ 17 19 11 18 14 10 12 13 16 15 ]


## R

### Original Fisher-Yates version

fisheryatesshuffle <- function(n)
{
pool <- seq_len(n)
a <- c()
while(length(pool) > 0)
{
k <- sample.int(length(pool), 1)
a <- c(a, pool[k])
pool <- pool[-k]
}
a
}


### Knuth variation

fisheryatesknuthshuffle <- function(n)
{
a <- seq_len(n)
while(n >=2)
{
k <- sample.int(n, 1)
if(k != n)
{
temp <- a[k]
a[k] <- a[n]
a[n] <- temp
}
n <- n - 1
}
a
}

#Example usage:
fisheryatesshuffle(6)                # e.g. 1 3 6 2 4 5
x <- c("foo", "bar", "baz", "quux")
x[fisheryatesknuthshuffle(4)]        # e.g. "bar"  "baz"  "quux" "foo"


### Short version

After accounting for R being 1-indexed rather than 0-indexed, it's not hard to implement the pseudo-code given in the task almost exactly:

knuth <- function(vec)
{
last <- length(vec)
if(last >= 2)
{
for(i in last:2)
{
j <- sample(seq_len(i), size = 1)
vec[c(i, j)] <- vec[c(j, i)]
}
}
vec
}
#Demonstration:
knuth(integer(0))
knuth(c(10))
replicate(10, knuth(c(10, 20)))
replicate(10, knuth(c(10, 20, 30)))
knuth(c("Also", "works", "for", "strings"))

Output:
> knuth(integer(0))
integer(0)
> knuth(c(10))
 10
> replicate(10, knuth(c(10, 20)))
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]   20   20   10   10   20   10   20   10   20    10
[2,]   10   10   20   20   10   20   10   20   10    20
> replicate(10, knuth(c(10, 20, 30)))
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]   30   10   20   20   30   30   10   30   10    10
[2,]   10   20   30   10   10   10   20   20   20    20
[3,]   20   30   10   30   20   20   30   10   30    30
> knuth(c("Also", "works", "for", "strings"))
 "strings" "Also"    "for"     "works"

## Racket

#lang racket

(define (swap! vec i j)
(let ([tmp (vector-ref vec i)])
(vector-set! vec i (vector-ref vec j))
(vector-set! vec j tmp)))

(define (knuth-shuffle x)
(if (list? x)
(vector->list (knuth-shuffle (list->vector x)))
(begin (for ([i (in-range (sub1 (vector-length x)) 0 -1)])
(define r (random (+ i 1)))
(swap! x i r))
x)))

(knuth-shuffle '(1 2 3 4))


## Raku

(formerly Perl 6)

Works with: Rakudo version #21 "Seattle"
sub shuffle (@a is copy) {
for 1 ..^ @a -> $n { my$k = (0 .. $n).pick;$k == $n or @a[$k, $n] = @a[$n, $k]; } return @a; }  The shuffle is also built into the pick method on lists when you pass it a "whatever" for the number to pick: my @deck = @cards.pick(*);  ## REBOL REBOL [ Title: "Fisher-Yates" Purpose: {Fisher-Yates shuffling algorithm} ] fisher-yates: func [b [block!] /local n i j k] [ n: length? b: copy b i: n while [i > 1] [ if i <> j: random i [ error? set/any 'k pick b j change/only at b j pick b i change/only at b i get/any 'k ] i: i - 1 ] b ]  ## REXX ### version 0, card pips /*REXX program shuffles a deck of playing cards (with jokers) using the Knuth shuffle.*/ rank= 'A 2 3 4 5 6 7 8 9 10 J Q K' /*pips of the various playing cards. */ suit= '♣♠♦♥' /*suit " " " " " */ parse arg seed . /*obtain optional argument from the CL.*/ if datatype(seed,'W') then call random ,,seed /*maybe use for RANDOM repeatability.*/ say '══════════════════ getting a new deck out of the box ···' @.1= 'highJoker' /*good decks have a color joker, and a */ @.2= 'lowJoker' /* ··· black & white joker. */ cards=2 /*now, there're 2 cards are in the deck*/ do j =1 for length(suit) do k=1 for words(rank); cards=cards + 1 @.cards=substr(suit, j, 1)word(rank, k) end /*k*/ end /*j*/ call show say; say '══════════════════ shuffling' cards "cards ···" do s=cards by -1 to 2; ?=random(1,s); parse value @.? @.s with @.s @.? /* [↑] swap two cards in the deck. */ end /*s*/ call show exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ show: _=; do m=1 for cards; _=_ @.m; end /*m*/; say _; return  output ══════════════════ getting a new deck out of the box ··· highJoker lowJoker ♣A ♣2 ♣3 ♣4 ♣5 ♣6 ♣7 ♣8 ♣9 ♣10 ♣J ♣Q ♣K ♠A ♠2 ♠3 ♠4 ♠5 ♠6 ♠7 ♠8 ♠9 ♠10 ♠J ♠Q ♠K ♦A ♦2 ♦3 ♦4 ♦5 ♦6 ♦7 ♦8 ♦9 ♦10 ♦J ♦Q ♦K ♥A ♥2 ♥3 ♥4 ♥5 ♥6 ♥7 ♥8 ♥9 ♥10 ♥J ♥Q ♥K ══════════════════ shuffling 54 cards ··· ♣J ♦3 ♥5 ♣10 ♥2 ♥J ♣6 ♦4 ♠2 ♥8 ♥A ♠A ♣9 ♣5 ♠7 ♦6 ♥6 ♠10 ♥9 ♦2 lowJoker ♥3 ♠5 ♠K ♣K ♣8 ♣Q ♠Q ♣2 ♦8 ♠4 ♣7 ♦5 ♥K ♣A ♠6 ♠J ♦Q ♦7 ♠9 ♦10 ♦K ♣4 ♥7 ♣3 ♠3 highJoker ♦A ♥4 ♦J ♠8 ♦9 ♥Q ♥10  ### version 1, card names This version handles items with (leading/trailing/embedded) blanks in them, so parse isn't an option for shuffling. /*REXX program shuffles a deck of playing cards (with jokers) using the Knuth shuffle.*/ rank = 'ace deuce trey 4 5 6 7 8 9 10 jack queen king' /*use pip names for cards*/ suit = 'club spade diamond heart' /* " suit " " " */ say '══════════════════ getting a new deck out of the box ···' @.1= ' color joker' /*good decks have a color joker, and a */ @.2= ' b&w joker' /* ··· black & white joker. */ cards=2 /*now, there're 2 cards are in the deck*/ do j =1 for words(suit) do k=1 for words(rank); cards=cards+1 /*bump the card counter. */ @.cards=right(word(suit,j),7) word(rank,k) /*assign a card name. */ end /*k*/ end /*j*/ call show 'ace' /*inserts blank when an ACE is found.*/ say; say '══════════════════ shuffling' cards "cards ···" do s=cards by -1 to 2; ?=random(1,s); _=@.?; @.?=@.s; @.s=_ end /*s*/ /* [↑] swap two cards in the deck. */ call show exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ show: parse arg break; say /*get separator card, show blank line. */ do m=1 for cards /* [↓] traipse through the card deck. */ if pos(break,@.m)\==0 then say /*show a blank to read cards easier. */ say 'card' right(m, 2) '───►' @.m /*display a particular card from deck. */ end /*m*/ return  output ══════════════════ getting a new deck out of the box ··· card 1 ───► color joker card 2 ───► b&w joker card 3 ───► club ace card 4 ───► club deuce card 5 ───► club trey card 6 ───► club 4 card 7 ───► club 5 card 8 ───► club 6 card 9 ───► club 7 card 10 ───► club 8 card 11 ───► club 9 card 12 ───► club 10 card 13 ───► club jack card 14 ───► club queen card 15 ───► club king card 16 ───► spade ace card 17 ───► spade deuce card 18 ───► spade trey card 19 ───► spade 4 card 20 ───► spade 5 card 21 ───► spade 6 card 22 ───► spade 7 card 23 ───► spade 8 card 24 ───► spade 9 card 25 ───► spade 10 card 26 ───► spade jack card 27 ───► spade queen card 28 ───► spade king card 29 ───► diamond ace card 30 ───► diamond deuce card 31 ───► diamond trey card 32 ───► diamond 4 card 33 ───► diamond 5 card 34 ───► diamond 6 card 35 ───► diamond 7 card 36 ───► diamond 8 card 37 ───► diamond 9 card 38 ───► diamond 10 card 39 ───► diamond jack card 40 ───► diamond queen card 41 ───► diamond king card 42 ───► heart ace card 43 ───► heart deuce card 44 ───► heart trey card 45 ───► heart 4 card 46 ───► heart 5 card 47 ───► heart 6 card 48 ───► heart 7 card 49 ───► heart 8 card 50 ───► heart 9 card 51 ───► heart 10 card 52 ───► heart jack card 53 ───► heart queen card 54 ───► heart king ══════════════════ shuffling 54 cards ··· card 1 ───► spade ace card 2 ───► heart jack card 3 ───► heart ace card 4 ───► diamond 10 card 5 ───► spade 7 card 6 ───► club 10 card 7 ───► club trey card 8 ───► diamond deuce card 9 ───► diamond 7 card 10 ───► spade queen card 11 ───► heart queen card 12 ───► spade deuce card 13 ───► spade 9 card 14 ───► diamond 4 card 15 ───► diamond ace card 16 ───► heart 6 card 17 ───► club king card 18 ───► color joker card 19 ───► spade 6 card 20 ───► heart 5 card 21 ───► diamond 8 card 22 ───► heart 8 card 23 ───► club 7 card 24 ───► heart king card 25 ───► club jack card 26 ───► diamond jack card 27 ───► heart 9 card 28 ───► spade trey card 29 ───► spade jack card 30 ───► spade king card 31 ───► heart 10 card 32 ───► diamond king card 33 ───► diamond trey card 34 ───► heart deuce card 35 ───► heart 4 card 36 ───► diamond 5 card 37 ───► diamond 9 card 38 ───► spade 4 card 39 ───► club 4 card 40 ───► club 5 card 41 ───► spade 5 card 42 ───► club 9 card 43 ───► b&w joker card 44 ───► club 6 card 45 ───► heart 7 card 46 ───► spade 8 card 47 ───► diamond 6 card 48 ───► club deuce card 49 ───► diamond queen card 50 ───► club queen card 51 ───► club ace card 52 ───► heart trey card 53 ───► spade 10 card 54 ───► club 8  ### version 2 /* REXX --------------------------------------------------------------- * 05.01.2014 Walter Pachl * borrow one improvement from version 1 * 06.01.2014 removed -"- (many tests cost more than few "swaps") *--------------------------------------------------------------------*/ Call random ,,123456 /* seed for random */ Do i=1 To 10; a.i=i; End; /* fill array */ Call show 'In',10 /* show start */ do i = 10 To 2 By -1 /* shuffle */ j=random(i-1)+1; h=right(i,2) right(j,2) Parse Value a.i a.j With a.j a.i /* a.i <-> a.j */ Call show h,i /* show intermediate states */ end; Call show 'Out',10 /* show fomaö state */ Exit show: Procedure Expose a. Parse Arg txt,n ol=left(txt,6); Do k=1 To n; ol=ol right(a.k,2); End Say ol Return  Output: In 1 2 3 4 5 6 7 8 9 10 10 2 1 10 3 4 5 6 7 8 9 2 9 6 1 10 3 4 5 9 7 8 6 8 6 1 10 3 4 5 8 7 9 7 3 1 10 7 4 5 8 3 6 5 1 10 7 4 8 5 5 1 8 10 7 4 1 4 1 4 10 7 8 3 1 7 10 4 2 1 10 7 Out 10 7 4 8 1 5 3 9 6 2 ## Ring # Project : Knuth shuffle items = list(52) for n = 1 to len(items) items[n] = n next knuth(items) showarray(items) func knuth(items) for i = len(items) to 1 step -1 j = random(i-1) + 1 if i != j temp = items[i] items[i] = items[j] items[j] = temp ok next func showarray(vect) see "[" svect = "" for n = 1 to len(vect) svect = svect + vect[n] + " " next svect = left(svect, len(svect) - 1) see svect see "]" + nl [15 1 51 20 45 29 43 8 13 3 41 35 11 7 37 9 38 17 32 48 40 25 44 18 14 50 42 34 2 21 12 4 26 19 23 24 28 46 36 10 5 16 6 49 22 33 39 47 31 52 30 27]  ## Ruby Translation of: Tcl class Array def knuth_shuffle! j = length i = 0 while j > 1 r = i + rand(j) self[i], self[r] = self[r], self[i] i += 1 j -= 1 end self end end r = Hash.new(0) 100_000.times do |i| a = [1,2,3].knuth_shuffle! r[a] += 1 end r.keys.sort.each {|a| puts "#{a.inspect} => #{r[a]}"}  results in [1, 2, 3] => 16572 [1, 3, 2] => 16610 [2, 1, 3] => 16633 [2, 3, 1] => 16714 [3, 1, 2] => 16838 [3, 2, 1] => 16633 More idiomatic: class Array def knuth_shuffle! (length - 1).downto(1) do |i| j = rand(i + 1) self[i], self[j] = self[j], self[i] end self end end  ## Run BASIC dim cards(52) for i = 1 to 52 ' make deck cards(i) = i next for i = 52 to 1 step -1 ' shuffle deck r = int((rnd(1)*i) + 1) if r <> i then hold = cards(r) cards(r) = cards(i) cards(i) = hold end if next print "== Shuffled Cards ==" ' print shuffled cards for i = 1 to 52 print cards(i);" "; if i mod 18 = 0 then print next print ## Rust Library: rand use rand::Rng; extern crate rand; fn knuth_shuffle<T>(v: &mut [T]) { let mut rng = rand::thread_rng(); let l = v.len(); for n in 0..l { let i = rng.gen_range(0, l - n); v.swap(i, l - n - 1); } } fn main() { let mut v: Vec<_> = (0..10).collect(); println!("before: {:?}", v); knuth_shuffle(&mut v); println!("after: {:?}", v); }  ## Scala def shuffle[T](a: Array[T]) = { for (i <- 1 until a.size reverse) { val j = util.Random nextInt (i + 1) val t = a(i) a(i) = a(j) a(j) = t } a }  ## Scheme A functional version, using lists (inefficient), somewhat unusual in reversing the entire initial sublist on each pass instead of just swapping: #!r6rs (import (rnrs base (6)) (srfi :27 random-bits)) (define (semireverse li n) (define (continue front back n) (cond ((null? back) front) ((zero? n) (cons (car back) (append front (cdr back)))) (else (continue (cons (car back) front) (cdr back) (- n 1))))) (continue '() li n)) (define (shuffle li) (if (null? li) () (let ((li-prime (semireverse li (random-integer (length li))))) (cons (car li-prime) (shuffle (cdr li-prime))))))  A mutable version, using vectors (efficient): #!r6rs (import (rnrs base (6)) (srfi :27 random-bits)) (define (vector-swap! vec i j) (let ((temp (vector-ref vec i))) (vector-set! vec i (vector-ref vec j)) (vector-set! vec j temp))) (define (countdown n) (if (zero? n) () (cons n (countdown (- n 1))))) (define (vector-shuffle! vec) (for-each (lambda (i) (let ((j (random-integer i))) (vector-swap! vec (- i 1) j))) (countdown (vector-length vec))))  ## Scratch See Knuth's shuffle in action. Visit this Scratch implementation to see a demo and inspect its source. ## Seed7 $ include "seed7_05.s7i";

const type: intArray is array integer;

const proc: shuffle (inout intArray: a) is func
local
var integer: i is 0;
var integer: k is 0;
var integer: tmp is 0;
begin
for i range maxIdx(a) downto 2 do
k := rand(1, i);
tmp := a[i];
a[i] := a[k];
a[k] := tmp;
end for;
end func;

const proc: main is func
local
var intArray: a is 10 times 0;
var integer: i is 0;
begin
for key i range a do
a[i] := i;
end for;
shuffle(a);
for i range a do
write(i <& " ");
end for;
writeln;
end func;
Output:
7 5 6 8 3 10 9 4 2 1


## SenseTalk

set list to 1..9 -- a range, will become a list as needed
set last to the number of items in list

repeat with i = last down to 2 -- in SenseTalk, the first index in a list is 1
set j = random (1,i-1)
set [item i of list, item j of list] to [item j of list, item i of list] -- swap items
end repeat

put list
Output:
[8,9,7,3,4,5,1,2,6]


## Sidef

func knuth_shuffle(a) {
for i (a.len ^.. 1) {
var j = i.irand
a[i, j] = a[j, i]
}
return a
}

say knuth_shuffle(@(1..10))

Output:
[7, 4, 3, 8, 9, 6, 10, 2, 1, 5]


## Smalltalk

Works with: GNU Smalltalk
"The selector swap:with: is documented, but it seems not
implemented (GNU Smalltalk version 3.0.4); so here it is an implementation"
SequenceableCollection extend [
swap: i with: j [
|t|
t := self at: i.
self at: i put: (self at: j).
self at: j put: t.
]
].

Object subclass: Shuffler [
Shuffler class >> Knuth: aSequenceableCollection [
|n k|
n := aSequenceableCollection size.
[ n > 1 ] whileTrue: [
k := Random between: 1 and: n.
aSequenceableCollection swap: n with: k.
n := n - 1
]
]
].


Testing

"Test"
|c|
c := OrderedCollection new.
c addAll: #( 1 2 3 4 5 6 7 8 9 ).
Shuffler Knuth: c.
c display.


## SNOBOL4

* Library for random()
-include 'Random.sno'

*       # String -> array
define('s2a(str,n)i') :(s2a_end)
s2a     s2a = array(n); str = str ' '
sa1     str break(' ') . s2a<i = i + 1> span(' ') = :s(sa1)f(return)
s2a_end

*       # Array -> string
define('a2s(a)i') :(a2s_end)
a2s     a2s = a2s a<i = i + 1> ' ' :s(a2s)f(return)
a2s_end

*       # Knuth shuffle in-place
define('shuffle(a)alen,n,k,tmp') :(shuffle_end)
shuffle n = alen = prototype(a);
sh1     k = convert(random() * alen,'integer') + 1
eq(a<n>,a<k>) :s(sh2)
tmp = a<n>; a<n> = a<k>; a<k> = tmp
sh2     n = gt(n,1) n - 1 :s(sh1)
shuffle = a :(return)
shuffle_end

*       # Test and display
a = s2a('1 2 3 4 5 6 7 8 9 10',10)
output = a2s(a) '->'
shuffle(a)
output = a2s(a)
end
Output:
1 2 3 4 5 6 7 8 9 10 ->
2 10 4 9 1 5 6 8 7 3

## Stata

mata
function shuffle(a) {
n = length(a)
r = runiformint(1,1,1,1..n)
for (i=n; i>=2; i--) {
j = r[i]
x = a[i]
a[i] = a[j]
a[j] = x
}
return(a)
}

shuffle(1..10)
end


Output

        1    2    3    4    5    6    7    8    9   10
+---------------------------------------------------+
1 |   8   10    9    1    7    2    6    4    3    5  |
+---------------------------------------------------+

## Swift

Version that works in Swift 5.x and probably above. This version works for any mutable bidirectional collection although O(n) time complexity can only be guaranteed for a RandomAccessCollection where the index meets the Apple requirements for O(1) access to elements.

Also has the advantage that it implemented the algorithm as written at the top of this page i.e. it counts down from the end and picks the random element from the part of the array that has not yet been traversed.

extension BidirectionalCollection where Self: MutableCollection
{
mutating func shuffleInPlace()
{
var index = self.index(before: self.endIndex)
while index != self.startIndex
{
// Note the use of ... below. This makes the current element eligible for being selected
let randomInt = Int.random(in: 0 ... self.distance(from: startIndex, to: index))
let randomIndex = self.index(startIndex, offsetBy: randomInt)
self.swapAt(index, randomIndex)
index = self.index(before: index)
}
}
}

var a = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
a.shuffleInPlace()
print(a)

Output:
[1, 5, 2, 7, 6, 0, 9, 8, 4, 3]

Simple version (any Swift version): Extend Array with shuffle methods; using arc4random_uniform from C stdlib:

import func Darwin.arc4random_uniform

extension Array {

func shuffle() -> Array {

var result = self; result.shuffleInPlace(); return result
}

mutating func shuffleInPlace() {

for i in 1 ..< count { swap(&self[i], &self[Int(arc4random_uniform(UInt32(i+1)))]) }
}

}

// Swift 2.0:
print([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())
// Swift 1.x:
//println([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())

Output:
[8, 7, 2, 1, 6, 10, 5, 3, 4, 9]

Generic version (any Swift version): While the above code is generic in that it works with arrays of any element type, we can use generic global functions to define shuffling for any mutable collection with random-access index type which is far more generic than the above code:

import func Darwin.arc4random_uniform

func shuffleInPlace<T: MutableCollectionType where T.Index: RandomAccessIndexType>(inout collection: T) {

let i0 = collection.startIndex

for i in i0.successor() ..< collection.endIndex {

arc4random_uniform(numericCast(
i0.distanceTo()
)+1)
))

swap(&collection[i], &collection[j])
}
}

func shuffle<T: MutableCollectionType where T.Index: RandomAccessIndexType>(collection: T) -> T {

var result = collection

shuffleInPlace(&result)

return result
}

// Swift 2.0:
print(shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
// Swift 1.x:
//println(shuffle([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))

Output:
[2, 5, 7, 1, 6, 10, 4, 3, 8, 9]
Works with: Swift version 2.0
While the above solutions work with Swift 2.0 as they are, we can use Swift 2.0's Protocol Oriented Programming features to add shuffling methods to any mutable collection that has a random-access index:
import func Darwin.arc4random_uniform

// Define a protocol for shuffling:

protocol Shufflable {

@warn_unused_result (mutable_variant="shuffleInPlace")
func shuffle() -> Self

mutating func shuffleInPlace()

}

// Provide a generalized implementation of the shuffling protocol for any mutable collection with random-access index:

extension Shufflable where Self: MutableCollectionType, Self.Index: RandomAccessIndexType {

func shuffle() -> Self {

var result = self

result.shuffleInPlace()

return result
}

mutating func shuffleInPlace() {

let i0 = startIndex

for i in i0+1 ..< endIndex {

arc4random_uniform(numericCast(
i0.distanceTo(i)
)+1)
))

swap(&self[i], &self[j])
}
}

}

// Declare Array's conformance to Shufflable:

extension Array: Shufflable
{ /* Implementation provided by Shufflable protocol extension */ }

print([1, 2, 3, 4, 5, 6, 7, 8, 9, 10].shuffle())

Output:
[3, 1, 5, 6, 7, 8, 10, 2, 4, 9]

## Tcl

proc knuth_shuffle lst {
set j [llength $lst] for {set i 0} {$j > 1} {incr i;incr j -1} {
set r [expr {$i+int(rand()*$j)}]
set t [lindex $lst$i]
lset lst $i [lindex$lst $r] lset lst$r $t } return$lst
}

% knuth_shuffle {1 2 3 4 5}
2 1 3 5 4
% knuth_shuffle {1 2 3 4 5}
5 2 1 4 3
% knuth_shuffle {tom dick harry peter paul mary}
tom paul mary harry peter dick


As a test of skewing (an indicator of a poor implementation) this code was used:

% for {set i 0} {$i<100000} {incr i} { foreach val [knuth_shuffle {1 2 3 4 5}] pos {pos0 pos1 pos2 pos3 pos4} { incr tots($pos) $val } } % parray tots tots(pos0) = 300006 tots(pos1) = 300223 tots(pos2) = 299701 tots(pos3) = 299830 tots(pos4) = 300240  ## TI-83 BASIC Input L1, output L2. :"SHUFFLE" :L1→L2 :dim(L2)→A :For(B,1,dim(L2)-1) :randInt(1,A)→C :L2(C)→D :L2(A)→L2(C) :D→L2(A) :A-1→A :End :DelVar A :DelVar B :DelVar C :DelVar D :Return  ## Transd #lang transd MainModule: { // Define an abstract type Vec to make the shuffling // function polymorphic Vec: typedef(Lambda<:Data Bool>(λ d :Data() (starts-with (_META_type d) "Vector<"))), kshuffle: (λ v Vec() locals: rnd 0 (for n in Range( (- (size v) 1) 0) do (= rnd (randr (to-Int n))) (with tmp (cp (get v n)) (set-el v n (get v rnd)) (set-el v rnd tmp)) ) (lout v) ), _start: (λ (with v [10,20,30,40,50,60,70,80,90,100] (lout "Original:\n" v) (lout "Shuffled:") (kshuffle v)) (lout "") (with v ["A","B","C","D","E","F","G","H"] (lout "Original:\n" v) (lout "Shuffled:") (kshuffle (cp v)) // Transd has a built-in function that performs the same // kind of random shuffle (lout "Built-in shuffle:") (lout (shuffle v))) ) }  Output: Original: [10, 20, 30, 40, 50, 60, 70, 80, 90, 100] Shuffled: [20, 60, 100, 80, 70, 10, 50, 90, 40, 30] Original: ["A", "B", "C", "D", "E", "F", "G", "H"] Shuffled: ["G", "A", "D", "B", "F", "E", "C", "H"] Built-in shuffle: ["A", "E", "C", "H", "G", "F", "B", "D"]  ## TUSCRIPT $$MODE TUSCRIPT oldnumbers=newnumbers="",range=20 LOOP nr=1,#range oldnumbers=APPEND(oldnumbers,nr) ENDLOOP PRINT "before ",oldnumbers LOOP r=#range,1,-1 RANDNR=RANDOM_NUMBERS (1,#r,1) shuffle=SELECT (oldnumbers,#randnr,oldnumbers) newnumbers=APPEND(newnumbers,shuffle) ENDLOOP PRINT "after ",newnumbers Output: before 1'2'3'4'5'6'7'8'9'10'11'12'13'14'15'16'17'18'19'20 after 7'16'13'11'1'9'15'4'18'14'3'12'17'8'19'20'6'5'2'10  ## uBasic/4tH PRINT "before:" FOR L = 0 TO 51 @(L) = L PRINT @(L); " "; NEXT FOR L = 51 TO 0 STEP -1 C = RND(L + 1) IF C # L THEN PUSH @(C), L, @(L), C GOSUB 100 ENDIF NEXT PRINT : PRINT "after:" FOR L = 0 TO 51 PRINT @(L); " "; NEXT PRINT END 100 @(POP()) = POP() : @(POP()) = POP() : RETURN  Output: before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 after: 19 4 49 9 27 35 50 11 2 29 22 48 33 15 17 42 47 28 41 18 34 21 30 39 3 8 23 12 36 26 0 46 7 44 13 14 16 40 10 25 31 32 51 24 20 38 45 6 43 1 5 37 ## UNIX Shell Works with: ksh93 Works with: pdksh # Shuffle array[@]. function shuffle { integer i j t ((i =${#array[@]}))
while ((i > 1)); do
((j = RANDOM))                 # 0 <= j < 32768
((j < 32768 % i)) && continue  # no modulo bias
((j %= i))                     # 0 <= j < i

((i -= 1))
((t = array[i]))
((array[i] = array[j]))
((array[j] = t))
done
}

# Test program.
set -A array 11 22 33 44 55 66 77 88 99 110
shuffle
echo "${array[@]}"  ## Ursala This function works on lists of any type and length, including character strings. shuffle = @iNX ~&l->r ^jrX/~&l ~&lK8PrC test program: #cast %s example = shuffle 'abcdefghijkl' Output: 'keacfjlbdigh' ## VBA Private Sub Knuth(Optional ByRef a As Variant) Dim t As Variant, i As Integer If Not IsMissing(a) Then For i = UBound(a) To LBound(a) + 1 Step -1 j = Int((UBound(a) - LBound(a) + 1) * Rnd + LBound(a)) t = a(i) a(i) = a(j) a(j) = t Next i End If End Sub Public Sub program() Dim b As Variant, c As Variant, d As Variant, e As Variant Randomize 'imagine an empty array on this line b = [{10}] c = [{10, 20}] d = [{10, 20, 30}] e = [{11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22}] f = [{"This ", "is ", "a ", "test"}] Debug.Print "Before:" Knuth 'feeding an empty array ;) Debug.Print "After: " Debug.Print "Before:"; For Each i In b: Debug.Print i;: Next i: Debug.Print Knuth b Debug.Print "After: "; For Each i In b: Debug.Print i;: Next i: Debug.Print Debug.Print "Before:"; For Each i In c: Debug.Print i;: Next i: Debug.Print Knuth c Debug.Print "After: "; For Each i In c: Debug.Print i;: Next i: Debug.Print Debug.Print "Before:"; For Each i In d: Debug.Print i;: Next i: Debug.Print Knuth d Debug.Print "After: "; For Each i In d: Debug.Print i;: Next i: Debug.Print Debug.Print "Before:"; For Each i In e: Debug.Print i;: Next i: Debug.Print Knuth e Debug.Print "After: "; For Each i In e: Debug.Print i;: Next i: Debug.Print Debug.Print "Before:"; For Each i In f: Debug.Print i;: Next i: Debug.Print Knuth f Debug.Print "After: "; For Each i In f: Debug.Print i;: Next i: Debug.Print End Sub  Output: Before: After: Before: 10 After: 10 Before: 10 20 After: 10 20 Before: 10 20 30 After: 20 10 30 Before: 11 12 13 14 15 16 17 18 19 20 21 22 After: 22 12 15 20 19 11 13 21 16 17 14 18 Before:This is a test After: a This testis  ## VBScript Implementation function shuffle( a ) dim i dim r randomize timer for i = lbound( a ) to ubound( a ) r = int( rnd * ( ubound( a ) + 1 ) ) if r <> i then swap a(i), a(r) end if next shuffle = a end function sub swap( byref a, byref b ) dim tmp tmp = a a = b b = tmp end sub  Invocation dim a a = array( 1,2,3,4,5,6,7,8,9) wscript.echo "before: ", join( a, ", " ) shuffle a wscript.echo "after: ", join( a, ", " ) shuffle a wscript.echo "after: ", join( a, ", " ) wscript.echo "--" a = array( now(), "cow", 123, true, sin(1), 16.4 ) wscript.echo "before: ", join( a, ", " ) shuffle a wscript.echo "after: ", join( a, ", " ) shuffle a wscript.echo "after: ", join( a, ", " )  Output: before: 1, 2, 3, 4, 5, 6, 7, 8, 9 after: 6, 4, 1, 2, 7, 3, 5, 8, 9 after: 8, 7, 3, 2, 6, 5, 9, 1, 4 -- before: 16/02/2010 5:46:58 PM, cow, 123, True, 0.841470984807897, 16.4 after: True, 16.4, 16/02/2010 5:46:58 PM, 123, cow, 0.841470984807897 after: 16.4, 16/02/2010 5:46:58 PM, 123, 0.841470984807897, True, cow  ## Vedit macro language The shuffle routine in Playing Cards shuffles text lines in edit buffer. This example shuffles numeric registers #0 to #19. The output will be inserted in current edit buffer. // Test main #90 = Time_Tick // seed for random number generator #99 = 20 // number of items in the array IT("Before:") IN for (#100 = 0; #100 < #99; #100++) { #@100 = #100 Num_Ins(#@100, LEFT+NOCR) IT(" ") } IN Call("SHUFFLE_NUMBERS") IT("After:") IN for (#100 = 0; #100 < #99; #100++) { Num_Ins(#@100, LEFT+NOCR) IT(" ") } IN Return //-------------------------------------------------------------- // Shuffle numeric registers #0 to #nn // #99 = number of registers to shuffle (nn-1) // :SHUFFLE_NUMBERS: for (#91 = #99-1; #91 > 0; #91--) { Call("RANDOM") #101 = Return_Value #102 = #@101; #@101 = #@91; #@91 = #102 } Return //-------------------------------------------------------------- // Generate random numbers in range 0 <= Return_Value < #91 // #90 = Seed (0 to 0x7fffffff) // #91 = Scaling (0 to 0x10000) // :RANDOM: #92 = 0x7fffffff / 48271 #93 = 0x7fffffff % 48271 #90 = (48271 * (#90 % #92) - #93 * (#90 / #92)) & 0x7fffffff Return ((#90 & 0xffff) * #91 / 0x10000) Output: Before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 After: 9 13 8 18 10 1 17 15 0 16 14 19 3 2 7 11 6 4 5 12  ## V (Vlang) Updated to Vlang version 0.2.2 import rand import rand.seed fn shuffle(mut arr []int) { for i := arr.len - 1; i >= 0; i-- { j := rand.intn(i + 1) arr[i], arr[j] = arr[j], arr[i] } println('After Shuffle:$arr')
}

fn main() {
seed_array := seed.time_seed_array(2)
rand.seed(seed_array)
mut arr := [6, 9, 1, 4]
println('Input: $arr') shuffle(mut arr) shuffle(mut arr) println('Output:$arr')
}

Output:
Input: [6, 9, 1, 4]
After Shuffle: [6, 1, 4, 9]
After Shuffle: [4, 9, 1, 6]
Output: [4, 9, 1, 6]

## Wren

import "random" for Random

var rand = Random.new()

var knuthShuffle = Fn.new { |a|
var i = a.count - 1
while (i >= 1) {
var j = rand.int(i + 1)
var t = a[i]
a[i] = a[j]
a[j] = t
i = i - 1
}
}

var tests = [ [], , [10, 20], [10, 20, 30] ]
for (a in tests) {
var b = a.toList // store original order
knuthShuffle.call(a)
System.print("%(b) -> %(a)")
}

Output:

Sample run:

[] -> []
 -> 
[10, 20] -> [20, 10]
[10, 20, 30] -> [30, 10, 20]


## XPL0

proc Shuffle(Array, Items, BytesPerItem);
int  Array, Items, BytesPerItem;
int  I, J;
char Temp(8);
[for I:= Items-1 downto 1 do
[J:= Ran(I+1);      \range [0..I]
CopyMem(Temp, Array+I*BytesPerItem, BytesPerItem);
CopyMem(Array+I*BytesPerItem, Array+J*BytesPerItem, BytesPerItem);
CopyMem(Array+J*BytesPerItem, Temp, BytesPerItem);
];
];

string 0;       \use zero-terminated strings
int A;  char B;  real C;
int I;
[A:= [1, 2, 3, 4, 5];
Shuffle(A, 5, 4 \bytes per int\);
for I:= 0 to 5-1 do
[IntOut(0, A(I));  ChOut(0, ^ )];
CrLf(0);
B:= "12345";
Shuffle(B, 5, 1 \byte per char\);
for I:= 0 to 5-1 do
[ChOut(0, B(I));  ChOut(0, ^ )];
CrLf(0);
C:= [1., 2., 3., 4., 5.];
Shuffle(addr C(0), 5, 8 \bytes per real\);
for I:= 0 to 5-1 do
[RlOut(0, C(I));  ChOut(0, ^ )];
CrLf(0);
A:= ;
Shuffle(A, 1, 4 \bytes per int\);
for I:= 0 to 1-1 do
[IntOut(0, A(I));  ChOut(0, ^ )];
CrLf(0);
]
Output:
2 4 1 5 3
1 3 4 5 2
5.00000     4.00000     2.00000     1.00000     3.00000
10


## Yabasic

// Rosetta Code problem: https://www.rosettacode.org/wiki/Ramsey%27s_theorem
// by Jjuanhdez, 06/2022

dim array(52)
for i = 1 to arraysize(array(),1) : array(i) = i : next i

print "Starting array"
for i = 1 to arraysize(array(),1)
print array(i) using "####";
next i

KnuthShuffle(array())

print "\n\nAfter Knuth shuffle downwards"
for i = 1 to arraysize(array(),1)
print array(i) using "####";
next i
print
end

sub KnuthShuffle(a())
local i, j, t, lb, ub
lb = 1
ub = arraysize(a(),1) - lb

for i = lb to ub
j = round(ran(i +1))
t = a(lb + i)
a(lb + i) = a(lb + j)
a(lb + j) = t
next i
end sub

## zkl

Two versions, imperative and functional, same results. xs has to be a mutable list.

fcn kshuffle(xs){
foreach i in ([xs.len()-1..1,-1]){ xs.swap(i,(0).random(0,i+1)) }
xs
}
fcn kshufflep(xs){
[xs.len()-1..1,-1].pump(Void,'wrap(i){ xs.swap(i,(0).random(0,i+1)) })
xs
}
var ns=(1).pump(10,List).copy() // [1..10] made mutable
kshuffle(ns)  //-->L(6,3,8,2,4,5,10,9,1,7)

ns="this is a test foo bar hoho".split(" ").copy();
kshufflep(ns)  //-->L("a","bar","hoho","foo","test","is","this")
`