# Knuth shuffle

(Redirected from Knuth Shuffle)
Knuth shuffle
You are encouraged to solve this task according to the task description, using any language you may know.

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 ${\displaystyle \leq }$ j ${\displaystyle \leq }$ 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] [10]
[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.)

## 360 Assembly

Translation of: BBC BASIC
 *        Knuth shuffle             02/11/2015KNUTHSH  CSECT         USING  KNUTHSH,R15         LA     R6,1               i=1LOOPI1   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      LOOPI1ELOOPI1  LA     R7,CARDS           n=cardsLOOPN    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      LOOPNELOOPN   LA     R6,1               i=1         LA     R8,PG              [email protected]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      LOOPI2ELOOPI2  XPRNT  PG,80              print buffer         XR     R15,R15            set return code         BR     R14                return to callerCARDS    EQU    20                 number of cardsPACK     DS     (CARDS+1)C         pack of cardsTMP      DS     C                  temp for swapPG       DC     CL80' '            bufferXD       DS     CL12               to decimalRANDSEED 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


## 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              *//*********************************/.datasMessResult:      .asciz "Value  : @ \n"szCarriageReturn: .asciz "\n" .align 4TableNumber:         .quad   1,2,3,4,5,6,7,8,9,10                     .equ NBELEMENTS, (. - TableNumber) / 8/*********************************//* UnInitialized data            *//*********************************/.bsssZoneConversion:         .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 x3,01:                                           // 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 x3,02:                                           // 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 szCarriageReturnqAdrsMessResult:          .quad sMessResultqAdrTableNumber:          .quad TableNumberqAdrsZoneConversion:      .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 index1:    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 value100:    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)               (randomm 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)) ## Ada 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 Ada.Text_IO.Put(Integer'Image(Integer_List(I))); end loop; Integer_Shuffle(List => Integer_List); Ada.Text_IO.New_Line; for I in Integer_List'Range loop Ada.Text_IO.Put(Integer'Image(Integer_List(I))); end loop;end Test_Shuffle; ## Aime The shuffle function works on any type (the lists are heterogenous). voidshuffle(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:( [20]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 iend repeatcopy {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 iend 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: on shuffle(array) repeat with i from (count array) to 2 by -1 set j to (random number from 1 to i) if (j < i) then tell array's item i set array's item i to array's item j set array's item j to it end tell end if end repeat return arrayend shuffle set array to {"Alpha", "Bravo", "Charlie", "Delta", "Echo", "Foxtrot", "Golf", "Hotel", "India", "Juliett", "Kilo", "Lima", "Mike"}shuffle(array) Output: eg. {"Lima", "Kilo", "Juliett", "Mike", "Echo", "Foxtrot", "Hotel", "Charlie", "Alpha", "India", "Delta", "Bravo", "Golf"} If the list to be shuffled is very long, using a straight list variable and calling the random number function that number of times could take quite a while. In AppleScript, it's actually very much faster to create another list containing the equivalent number of indices, refer to both list variables as properties of a script object, use the some specifier to select items at random from the index list, and replace the index list each time! If the length of the target list in the script above is doubled 8 times, that shuffle takes about 2.55 seconds on my current machine. The version below only takes around 0.045 seconds. on shuffle(theArray) script o property array : theArray property idxArray : {} end script set arrayLength to (count theArray) repeat with i from arrayLength to 1 by -1 set end of o's idxArray to i end repeat repeat with i from arrayLength to 2 by -1 set j to some item of o's idxArray if (j < i) then tell o's array's item i set o's array's item i to o's array's item j set o's array's item j to it end tell end if set o's idxArray to rest of o's idxArray end repeat return theArrayend shuffle set array to {"Alpha", "Bravo", "Charlie", "Delta", "Echo", "Foxtrot", "Golf", "Hotel", "India", "Juliett", "Kilo", "Lima", "Mike"}repeat 8 times set array to array & arrayend repeat shuffle(array) ### 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 lstend enumFromTo -- foldr :: (a -> b -> a) -> a -> [b] -> aon 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 tellend foldr -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Scripton mReturn(f) if class of f is script then f else script property |λ| : f end script end ifend 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 *//*********************************/.datasMessResult: .ascii "Value : "sMessValeur: .fill 11, 1, ' ' @ size => 11szCarriageReturn: .asciz "\n" .align 4iGraine: .int 123456.equ NBELEMENTS, 10TableNumber: .int 1,2,3,4,5,6,7,8,9,10 /*********************************//* UnInitialized data *//*********************************/.bss /*********************************//* code section *//*********************************/.text.global main main: @ entry of program ldr r0,iAdrTableNumber @ address number table mov r1,#NBELEMENTS @ number of élements bl knuthShuffle ldr r2,iAdrTableNumber mov r3,#01: @ loop display table ldr r0,[r2,r3,lsl #2] ldr r1,iAdrsMessValeur @ display value bl conversion10 @ call function ldr r0,iAdrsMessResult bl affichageMess @ display message add r3,#1 cmp r3,#NBELEMENTS - 1 ble 1b ldr r0,iAdrszCarriageReturn bl affichageMess /* 2e shuffle */ ldr r0,iAdrTableNumber @ address number table mov r1,#NBELEMENTS @ number of élements bl knuthShuffle ldr r2,iAdrTableNumber mov r3,#02: @ loop display table ldr r0,[r2,r3,lsl #2] ldr r1,iAdrsMessValeur @ display value bl conversion10 @ call function ldr r0,iAdrsMessResult bl affichageMess @ display message add r3,#1 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 iAdrsMessValeur: .int sMessValeuriAdrszCarriageReturn: .int szCarriageReturniAdrsMessResult: .int sMessResultiAdrTableNumber: .int TableNumber /******************************************************************//* 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 index1: 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] add r2,#1 @ next number 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 addne r2,r2,#1 @ else add 1 in the length 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, 10conversion10: push {r1-r4,lr} @ save registers mov r3,r1 mov r2,#LGZONECAL 1: @ start loop bl divisionpar10U @unsigned r0 <- dividende. quotient ->r0 reste -> r1 add r1,#48 @ digit 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,#02: ldrb r1,[r3,r2] strb r1,[r3,r4] add r2,#1 add r4,#1 cmp r2,#LGZONECAL ble 2b @ and move spaces in end on area mov r0,r4 @ result length mov r1,#' ' @ space3: strb r1,[r3,r4] @ store space in area add r4,#1 @ next position 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 r4,iAdriGraine ldr r2,[r4] ldr r3,iNbDep1 mul r2,r3,r2 ldr r3,iNbDep1 add r2,r2,r3 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/*****************************************************/iAdriGraine: .int iGraine iNbDep1: .int 0x343FDiNbDep2: .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 2f1: @ 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: @(arr){ if [size arr]=0 -> return #() loop [range [size arr]-1 0] { j: random 0 & swap! arr & j }} print|knuth #()print|knuth #(10)print|knuth #(10 20)print|knuth #(10 20 30) Output: #() #(10) #(20 10) #(10 30 20) ## 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} ## AutoIt  Dima[10]ConsoleWrite('array before permutation:' & @CRLF)For $i = 0 To 9$a[$i] = Random(20,100,1) ConsoleWrite($a[$i] & ' ')NextConsoleWrite(@CRLF) _Permute($a)ConsoleWrite('array after permutation:' & @CRLF)For $i = 0 To UBound($a) -1	ConsoleWrite($a[$i] & ' ')NextConsoleWrite(@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] = $tmp NextEndFunc  Output:  array before permutation: 43 57 37 20 97 98 69 76 97 70 array after permutation: 57 69 97 70 37 97 20 76 43 98  ## AWK Many arrays in AWK have the first index at 1. This example shows how to shuffle such arrays. The elements can be integers, floating-point numbers, or strings. # Shuffle an _array_ with indexes from 1 to _len_.function shuffle(array, len, i, j, t) { for (i = len; i > 1; i--) { # j = random integer from 1 to i j = int(i * rand()) + 1 # swap array[i], array[j] t = array[i] array[i] = array[j] array[j] = t }} # Test program.BEGIN { len = split("11 22 33 44 55 66 77 88 99 110", array) shuffle(array, len) for (i = 1; i < len; i++) printf "%s ", array[i] printf "%s\n", array[len]} ## BASIC RANDOMIZE TIMER DIM cards(51) AS INTEGERDIM L0 AS LONG, card AS LONG PRINT "before:"FOR L0 = 0 TO 51 cards(L0) = L0 PRINT LTRIM$(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$(cards(L0))); " ";NEXTPRINT Output:  before: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 after: 27 14 37 35 3 44 25 38 46 1 22 49 2 51 16 32 20 30 4 33 36 6 31 21 41 34 9 13 0 50 47 48 40 39 7 18 19 26 24 10 29 5 12 28 11 17 43 45 8 23 42 15  ### Applesoft BASIC As mentioned in the Sinclair ZX81 BASIC solution, for very small positive integer values, a string is a much more memory-efficient array, but here is an example of an array with numbers. Line 150 initializes and prints each element in the array. Line 190 performs the swap of the elements.  100 : 110 REM KNUTH SHUFFLE 120 : 130 DIM A(25) 140 FOR I = 1 TO 25 150 A(I) = I: PRINT A(I);" ";: NEXT I 160 PRINT : PRINT 170 FOR I = 25 TO 2 STEP - 1 180 J = INT ( RND (1) * I + 1) 190 T = A(I):A(I) = A(J):A(J) = T: NEXT I 200 FOR I = 1 TO 25 210 PRINT A(I);" ";: NEXT I 220 END  Output: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21 22 23 24 25 When it has finished, the screen will show (for example): 20 5 6 9 15 23 22 8 4 24 7 11 16 21 2 17 14 10 19 13 12 18 1 3 25 ### Sinclair ZX81 BASIC For very small positive integer values, a string (which can be treated as an array of bytes) is much more memory-efficient than an array of numbers. In this program we shuffle a string consisting of the letters 'A' to 'Z'. The ZX81 is slow enough that we can watch the shuffle happening in real time, with items switching to inverse video display as they are shuffled. (This can be done, in the ZX81 character set, by setting the high bit in the character code.) Line 10 seeds the pseudo-random number generator. Note that strings (and arrays) are indexed from 1. The program works with the unexpanded (1k RAM) ZX81.  10 RAND 20 LET A$="" 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

## 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

## 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

## 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[20]; 	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.

## 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} ${t}) endforeach(i) # Convert array to list. set(answer) foreach(i RANGE 1${last})    list(APPEND answer ${ARGV${i}})  endforeach(i)  set("${var}"${answer} PARENT_SCOPE)endfunction(shuffle)

## 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()

## 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 Systemusing Listusing 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]}  endend 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   PRINTEND PROGRAM 

## Euphoria

Translation of: BASIC
sequence cardscards = 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 ifend 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 iDim 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) + 1Next 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 bufferWhile InKey <> "" : WendPrint : Print "hit any key to end program"SleepEnd
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()

## Gambas

Public Sub Main()Dim iTotal As Integer = 40Dim iCount, iRand1, iRand2 As IntegerDim 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 [20]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 listprintln 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]

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"
"iebjhkcgfad"

An imperative implementation using arrays and the ST monad:

import Data.Array.STimport Data.STRefimport Control.Monadimport Control.Monad.STimport Control.Arrowimport 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) liftM2 (,) (readArray a k) (readArray a 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 Aend 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 :=: ?Aend 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&{[email protected][ {(|[email protected][)]} ])/@(,~(,[email protected]>:))@[email protected]# 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: (,~(,[email protected]>:))@[email protected]# 1+i.60 0 0 0 0 01 1 0 0 0 02 0 0 0 0 03 2 0 0 0 04 3 0 0 0 05 0 0 0 0 00 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&{[email protected][ {(|[email protected][)]} ] 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, (,~ (,. [email protected]>:))@[email protected]# can be replaced with |[email protected]; ;&~./@(,. [email protected]>:)@[email protected]#, and the swapping can be achieved using (<@C. >)/ instead of (2&{[email protected][ {(|[email protected][)]} ])/. With this approach, the data structure with the swapping indices and the original data could look like this:  (|[email protected]; ;&~./@(,. [email protected]>:)@[email protected]#)'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. >)/@(|[email protected]; ;&~./@(,. [email protected]>:)@[email protected]#) 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.95 6 7 8 9 10 11 12 13 Shuffle: KS A13 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 M11 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%$';'[email protected]'+--+---+----+---+|aA|bbB|cC%$|[email protected]|+--+---+----+---+ Shuffle KS L+--+----+---+---+|aA|cC%$|[email protected]|bbB|+--+----+---+---+

In J the shuffling of an arbitrary array can easily be implemented by the phrase ( ref http://www.jsoftware.com/jwiki/JPhrases/RandomNumbers ):

({[email protected]#)

Applied on the former examples:

({[email protected]#) A8 7 13 6 10 11 5 9 12    ({[email protected]#) 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    ({[email protected]#) L+----+---+--+---+|cC%$|bbB|aA|[email protected]|+----+---+--+---+ ## Java import java.util.Random; public static final Random gen = new Random(); // version for array of intspublic 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 referencespublic 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 inilib is loaded agglib is loaded [12 6 8 4 14 18 7 15 1 0 11 13 5 10 16 2 19 17 9 20 3]  ## 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 vendknuthshuffle!(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 = 9Dim 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)) = temp1Next i PrintFor 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 :tendto 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 :ashow :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 :resend 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 :aend to shuffle :a	for "i [count :a 2] 	[		make "a swap 1 + random :i :i :a	]	op :aend make "a ( list 1 2 3 4 5 6 7 8 9 10 )make "a shuffle :ashow :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 tend 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()           }  

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 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]); endend 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: [email protected]:~$ ./shuffle
9 2 7 3 6 8 4 5 1 10

## 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.lengthdeck = ArrayList(cardsLen)loop c_ = 0 to cardsLen - 1  deck.add(String(cards[c_]))  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.lengthdeck = ArrayList(cardsLen)loop c_ = 0 to cardsLen - 1  deck.add(String(cards[c_]))  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

import mathrandomize() proc shuffle[T](x: var seq[T]) =  for i in countdown(x.high, 0):    let j = random(i + 1)    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[9];  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  endend; procedure DisplayList(const a: tmylist);var  i : integer;Begin  for i := Low(a) to High(a) do    write(a[i]);  writelnend; { 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: ")      ?cardsfor i=52 to 1 by -1 do    integer r = rand(i)    {cards[r],cards[i]} = {cards[i],cards[r]}end forputs(1,"After:  ")      ?cardsputs(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 Methodfunction yates_shuffle($arr){$shuffled = Array();	while($arr){$rnd = array_rand($arr);$shuffled[] = $arr[$rnd];		array_splice($arr,$rnd, 1);	}	return $shuffled;} //The modern Durstenfeld-Knuth algorithmfunction knuth_shuffle(&$arr){	for($i=count($arr)-1;$i>0;$i--){		$rnd = mt_rand(0,$i);		list($arr[$i], $arr[$rnd]) = array($arr[$rnd], $arr[$i]);	}}

## 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
$A = 1, 2, 3, 4, 5Get-Random$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) = iNext 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 reducefrom 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[0]] + ys + [ht[0]] + 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 () -> Intdef 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] -> Stringdef 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

## 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 5x <- c("foo", "bar", "baz", "quux")x[fisheryatesknuthshuffle(4)]        # e.g. "bar"  "baz"  "quux" "foo"

## 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 showsay; 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 showexit /*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); [email protected].?; @.[email protected].s; @.s=_ end /*s*/ /* [↑] swap two cards in the deck. */call showexit /*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,nol=left(txt,6);Do k=1 To n; ol=ol right(a.k,2); EndSay olReturn 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] = nnextknuth(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 endend r = Hash.new(0)100_000.times do |i| a = [1,2,3].knuth_shuffle! r[a] += 1end 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 endend ## Run BASIC dim cards(52) for i = 1 to 52 ' make deck cards(i) = inext 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 ifnext print "== Shuffled Cards ==" ' print shuffled cardsfor i = 1 to 52 print cards(i);" "; if i mod 18 = 0 then printnextprint ## 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


## 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> = tmpsh2     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

matafunction 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

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 {         let j = i0.advancedBy(numericCast(                    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 {             let j = i0.advancedBy(numericCast(                        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 totstots(pos0) = 300006tots(pos1) = 300223tots(pos2) = 299701tots(pos3) = 299830tots(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  ## TUSCRIPT $$MODE TUSCRIPToldnumbers=newnumbers="",range=20LOOP 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 ENDIFNEXT PRINT : PRINT "after:"FOR L = 0 TO 51 PRINT @(L); " ";NEXTPRINTEND 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 =${#array[@]}))	while ((i > 1)); do		((j = RANDOM))                 # 0 <= j < 32768		((j < 32768 % i)) && continue  # no modulo bias		((j %= i))                     # 0 <= j < i 		((i -= 1))		((t = array[i]))		((array[i] = array[j]))		((array[j] = t))	done} # Test program.set -A array 11 22 33 44 55 66 77 88 99 110shuffleecho "${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 IfEnd SubPublic 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.PrintEnd 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 = aend function sub swap( byref a, byref b ) dim tmp tmp = a a = b b = tmpend sub Invocation dim aa = array( 1,2,3,4,5,6,7,8,9)wscript.echo "before: ", join( a, ", " )shuffle awscript.echo "after: ", join( a, ", " )shuffle awscript.echo "after: ", join( a, ", " )wscript.echo "--"a = array( now(), "cow", 123, true, sin(1), 16.4 )wscript.echo "before: ", join( a, ", " )shuffle awscript.echo "after: ", join( a, ", " )shuffle awscript.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:") INfor (#100 = 0; #100 < #99; #100++) { #@100 = #100 Num_Ins(#@100, LEFT+NOCR) IT(" ")}IN Call("SHUFFLE_NUMBERS") IT("After:") INfor (#100 = 0; #100 < #99; #100++) { Num_Ins(#@100, LEFT+NOCR) IT(" ")}INReturn //--------------------------------------------------------------// 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)) & 0x7fffffffReturn ((#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  ## Vlang import ( rand) fn shuffle(arr mut []int) { for i := arr.len - 1; i >= 0; i-- { j := rand.next(i + 1) temp := arr[i] arr[i] = arr[j] arr[j] = temp } println('After Shuffle: ' + arr.str())} fn main() { rand.seed(100) 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]

## 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")
`