# Sorting algorithms/Selection sort: Difference between revisions

Sorting algorithms/Selection sort
You are encouraged to solve this task according to the task description, using any language you may know.

Sorting Algorithm
This is a sorting algorithm.   It may be applied to a set of data in order to sort it.     For comparing various sorts, see compare sorts.   For other sorting algorithms,   see sorting algorithms,   or:

O(n logn) sorts

O(n log2n) sorts
Shell Sort

In this task, the goal is to sort an array (or list) of elements using the Selection sort algorithm. It works as follows:

First find the smallest element in the array and exchange it with the element in the first position, then find the second smallest element and exchange it with the element in the second position, and continue in this way until the entire array is sorted. Its asymptotic complexity is O(n2) making it inefficient on large arrays.

procedure Test_Selection_Sort is

```  type Integer_Array is array (Positive range <>) of Integer;
procedure Sort (A : in out Integer_Array) is
Min  : Positive;
Temp : Integer;
begin
for I in A'First..A'Last - 1 loop
Min := I;
for J in I + 1..A'Last loop
if A (Min) > A (J) then
Min := J;
end if;
end loop;
if Min /= I then
Temp    := A (I);
A (I)   := A (Min);
A (Min) := Temp;
end if;
end loop;
end Sort;
```
```  A : Integer_Array := (4, 9, 3, -2, 0, 7, -5, 1, 6, 8);
```

begin

```  Sort (A);
for I in A'Range loop
Put (Integer'Image (A (I)) & " ");
end loop;
```

end Test_Selection_Sort; </lang> Sample output:

```-5 -2  0  1  3  4  6  7  8  9
```

## ALGOL 68

Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386

<lang algol> MODE DATA = REF CHAR;

PROC in place selection sort = (REF[]DATA a)VOID: BEGIN

```  INT min;
DATA temp;
FOR i FROM LWB a TO UPB a DO
min := i;
FOR j FROM i + 1 TO UPB a DO
IF a [min] > a [j] THEN
min := j
FI
OD;
IF min /= i THEN
temp    := a [i];
a [i]   := a [min];
a [min] := temp
FI
OD
```

END # in place selection sort #;

[32]CHAR data := "big fjords vex quick waltz nymph"; [UPB data]DATA ref data; FOR i TO UPB data DO ref data[i] := data[i] OD; in place selection sort(ref data); FOR i TO UPB ref data DO print(ref data[i]) OD; print(new line); print((data)) </lang> Output:

```     abcdefghiijklmnopqrstuvwxyz
big fjords vex quick waltz nymph
```

## AutoHotkey

ahk forum: discussion <lang AutoHotkey>MsgBox % SelecSort("") MsgBox % SelecSort("xxx") MsgBox % SelecSort("3,2,1") MsgBox % SelecSort("dog,000000,xx,cat,pile,abcde,1,cat,zz,xx,z")

SelecSort(var) {  ; SORT COMMA SEPARATED LIST

```  StringSplit a, var, `,                ; make array, size = a0
```
```  Loop % a0-1 {
i := A_Index, mn := a%i%, j := m := i
Loop % a0-i {                      ; find minimum
j++
If (a%j% < mn)
mn := a%j%, m := j
}
t := a%i%, a%i% := a%m%, a%m% := t ; swap first with minimum
}
Loop % a0                             ; construct string from sorted array
sorted .= "," . a%A_Index%
Return SubStr(sorted,2)               ; drop leading comma
```

}</lang>

## AWK

<lang awk>function getminindex(gl, gi, gs) {

``` min = gl[gi]
gm = gi
for(gj=gi; gj <= gs; gj++) {
if ( gl[gj] < min ) {
min = gl[gj]
gm = gj
}
}
return gm
```

}

{

``` line[NR] = \$0
```

} END { # sort it with selection sort

``` for(i=1; i <= NR; i++) {
mi = getminindex(line, i, NR)
t = line[i]
line[i] = line[mi];
line[mi] = t
}
#print it
for(i=1; i <= NR; i++) {
print line[i]
}
```

}</lang>

## C

<lang c>#include <stdio.h>

int getminindex(int *a, int s, int b) {

``` int i, min=a[s], mi=s;
for(i=s; i < b; i++)
{
if ( a[i] < min ) { min = a[i]; mi = i; }
}
return mi;
```

}

void selectionsort(int *a, int s) {

``` int i, t, mi;
for(i=0; i<s ; i++)
{
mi = getminindex(a, i, s);
t = a[i]; a[i] = a[mi]; a[mi] = t;
}
```

}

int main() {

```  int ar[] = { 5, 200, 1, 65, 30, 99, 2, 0 };
int i;

selectionsort(ar, 8);
for(i=0; i<8; i++)
{
printf("%d\n", ar[i]);
}

return 0;
```

} </lang>

Sample output

```0
1
2
5
30
65
99
200
```

## C++

Compiler: g++ (version 4.3.2 20081105 (Red Hat 4.3.2-7))

<lang cpp>#include <algorithm>

1. include <iterator>

template<typename ForwardIterator> void selectionSort(ForwardIterator begin, ForwardIterator end) {

``` ForwardIterator i = begin;
while(i != end) {
ForwardIterator j = i;
ForwardIterator min = i;
while(j != end) {
if(*j < *min) {
min = j;
}
++j;
}
std::iter_swap(i, min);
++i;
}
```

}

</lang>

## Common Lisp

<lang lisp>(defun selection-sort-vector (array predicate)

``` (do ((length (length array))
(i 0 (1+ i)))
((eql i length) array)
(do ((mindex i)
(min (aref array i))
(j i (1+ j)))
((eql j length)
(rotatef (aref array i) (aref array mindex)))
(when (funcall predicate (aref array j) min)
(setf min (aref array j)
mindex j)))))
```

(defun selection-sort-list (list predicate)

``` (flet ((min-first (list)
(do ((before-min nil)
(min (first list))
(prev list (rest prev))
(curr (rest list) (rest curr)))
((endp curr)
(if (null before-min) list
(let ((min (cdr before-min)))
(rplacd before-min (cdr min))
(rplacd min list)
min)))
(when (funcall predicate (first curr) min)
(setf before-min prev
min (first curr))))))
(let ((result (min-first list)))
((endp (rest head)) result)
```

(defun selection-sort (sequence predicate)

``` (etypecase sequence
(list (selection-sort-list sequence predicate))
(vector (selection-sort-vector sequence predicate))))</lang>
```

Example use:

```> (selection-sort (list 8 7 4 3 2 0 9 1 5 6) '<)
(0 1 2 3 4 5 6 7 8 9)

> (selection-sort (vector 8 7 4 3 2 0 9 1 5 6) '>)
#(9 8 7 6 5 4 3 2 1 0)```

## D

<lang d> // Written in D 2.0.

import std.stdio;

void swap(T)(ref T lhs, ref T rhs) {

```   T temp = lhs;
lhs = rhs;
rhs = temp;
```

}

void selectionSort(T)(T[] data) {

```   foreach(i; 0..data.length) {
size_t minIndex = i;
foreach(j; i + 1..data.length) {
if(data[j] < data[minIndex]) {
minIndex = j;
}
}
swap(data[i], data[minIndex]);
}
```

}

void main() {

```   auto foo = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9, 3, 2];
selectionSort(foo);
writeln(foo);
```

} </lang>

## E

<lang e>def selectionSort := {

``` def cswap(c, a, b) {
def t := c[a]
c[a]  := c[b]
c[b]  := t
println(c)
}

def indexOfMin(array, first, last) {
var min := array[first]
var mini := first
for i in (first+1)..last {
if (array[i] < min) {
min := array[i]
mini := i
}
}
return mini
}
```
``` /** Selection sort (in-place). */
def selectionSort(array) {
def last := (array.size()-1)
for i in 0..(last - 1) {
cswap(array, i, indexOfMin(array, i + 1, last))
}
}
```

}</lang>

## Forth

<lang forth> defer less? ' < is less?

least ( start end -- least )
``` over cell+ do
i @ over @ less? if drop i then
cell +loop ;
```
selection ( array len -- )
``` cells over + tuck ( end start end )
cell- swap do   ( end )
i over least ( end least )
i @ over @ i ! swap !
cell +loop drop ;
```

create array 8 , 1 , 4 , 2 , 10 , 3 , 7 , 9 , 6 , 5 ,

array 10 selection array 10 cells dump </lang>

## Fortran

Works with: Fortran version 95 and later

<lang fortran> PROGRAM SELECTION

``` IMPLICIT NONE
```
``` INTEGER :: intArray(10) = (/ 4, 9, 3, -2, 0, 7, -5, 1, 6, 8 /)

WRITE(*,"(A,10I5)") "Unsorted array:", intArray
CALL Selection_sort(intArray)
WRITE(*,"(A,10I5)") "Sorted array  :", intArray

```

CONTAINS

``` SUBROUTINE Selection_sort(a)
INTEGER, INTENT(IN OUT) :: a(:)
INTEGER :: i, minIndex, temp
```
```   DO i = 1, SIZE(a)-1
minIndex = MINLOC(a(i:), 1) + i - 1
IF (a(i) > a(minIndex)) THEN
temp = a(i)
a(i) = a(minIndex)
a(minIndex) = temp
END IF
END DO
END SUBROUTINE Selection_sort
```

END PROGRAM SELECTION </lang> Output:

```Unsorted array:    4    9    3   -2    0    7   -5    1    6    8
Sorted array  :   -5   -2    0    1    3    4    6    7    8    9
```

<lang haskell>selectionSort [] = [] selectionSort (first:lst) = selectR first [] lst where

```  selectR small output [] = small : selectionSort output
selectR small output (x:xs) | x < small = selectR x (small:output) xs
| otherwise = selectR small (x:output) xs</lang>
```

## J

Create the following script and load it to a J session. <lang j>selectionSort=: verb define data=. y for_xyz. y do.

``` temp=. xyz_index }. data
nvidx=. xyz_index + temp i. <./ temp
data=. ((xyz_index, nvidx) { data) (nvidx, xyz_index) } data
```

end. data )</lang>

In an email discussion, Roger_Hui presented the following tacit code: <lang j> ix=: C.~ <@~.@(0, (i. <./))

```  ss1=: ({. , \$:@}.)@ix^:(*@#)
```

</lang>

To validate: <lang j> [data=. 6 15 19 12 14 19 0 17 0 14 6 15 19 12 14 19 0 17 0 14

```  selectionSort data
```

0 0 6 12 14 14 15 17 19 19

```  ss1 data
```

0 0 6 12 14 14 15 17 19 19 </lang>

## Java

This algorithm sorts in place. The call sort(array) will rearrange the array and not create a new one. <lang java>public static void sort(int[] nums){ for(int currentPlace = 0;currentPlace<nums.length-1;currentPlace++){ int smallest = Integer.MAX_VALUE; int smallestAt = currentPlace+1; for(int check = currentPlace; check<nums.length;check++){ if(nums[check]<smallest){ smallestAt = check; smallest = nums[check]; } } int temp = nums[currentPlace]; nums[currentPlace] = nums[smallestAt]; nums[smallestAt] = temp; } } </lang>

## MAXScript

```fn selectionSort arr =
(
local min = undefined
for i in 1 to arr.count do
(
min = i
for j in i+1 to arr.count do
(
if arr[j] < arr[min] then
(
min = j
)
)
swap arr[i] arr[min]
)
arr
)

data = selectionSort #(4, 9, 3, -2, 0, 7, -5, 1, 6, 8)
print data
```

## OCaml

<lang ocaml>let rec selection_sort = function

```   [] -> []
| first::lst ->
let rec select_r small output = function
[] -> small :: selection_sort output
| x::xs when x < small -> select_r x (small::output) xs
| x::xs                -> select_r small (x::output) xs
in
select_r first [] lst</lang>
```

## Perl

Translation of: Tcl

<lang perl>sub selection_sort

``` {my @a = @_;
foreach my \$i (0 .. \$#a - 1)
{my \$min = \$i + 1;
\$a[\$_] < \$a[\$min] and \$min = \$_ foreach \$min .. \$#a;
\$a[\$i] > \$a[\$min] and @a[\$i, \$min] = @a[\$min, \$i];}
return @a;}</lang>
```

## Python

<lang python>def selectionSort(lst):

```   for i in range(0,len(lst)-1):
mn = min(range(i,len(lst)), key=lst.__getitem__)
lst[i],lst[mn] = lst[mn],lst[i]
return lst</lang>
```

## R

For loop: <lang r> selectionsort.loop <- function(x) {

```  lenx <- length(x)
for(i in seq_along(x))
{
mini <- (i - 1) + which.min(x[i:lenx])
start_ <- seq_len(i-1)
x <- c(x[start_], x[mini], x[-c(start_, mini)])
}
x
```

} </lang> Recursive:

(A prettier solution, but, you may need to increase the value of options("expressions") to test it. Also, you may get a stack overflow if the length of the input vector is more than a few thousand.) <lang r> selectionsort.rec <- function(x) {

```  if(length(x) > 1)
{
mini <- which.min(x)
c(x[mini], selectionsort(x[-mini]))
} else x
```

} </lang>

## Ruby

Translation of: Tcl

<lang ruby>class Array

``` def selectionsort!
0.upto(length - 2) do |i|
(min_idx = i + 1).upto(length - 1) do |j|
if self[j] < self[min_idx]
min_idx = j
end
end
if self[i] > self[min_idx]
self[i], self[min_idx] = self[min_idx], self[i]
end
end
self
end
```

end ary = [7,6,5,9,8,4,3,1,2,0] ary.selectionsort!

1. => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]</lang>

## Standard ML

<lang sml>fun selection_sort [] = []

``` | selection_sort (first::lst) =
let
fun select_r small ([], output) = small :: selection_sort output
| select_r small (x::xs, output) =
if x < small then
select_r x (xs, small::output)
else
select_r small (xs, x::output)
in
select_r first (lst, [])
end</lang>
```

## Tcl

Uses `struct::list` package from
Library: tcllib

<lang tcl>package require Tcl 8.5 package require struct::list

proc selectionsort {A} {

```   set len [llength \$A]
for {set i 0} {\$i < \$len - 1} {incr i} {
set min_idx [expr {\$i + 1}]
for {set j \$min_idx} {\$j < \$len} {incr j} {
if {[lindex \$A \$j] < [lindex \$A \$min_idx]} {
set min_idx \$j
}
}
if {[lindex \$A \$i] > [lindex \$A \$min_idx]} {
struct::list swap A \$i \$min_idx
}
}
return \$A
```

}

puts [selectionsort {8 6 4 2 1 3 5 7 9}] ;# => 1 2 3 4 5 6 7 8 9</lang>

## Ursala

The selection_sort function is parameterized by a relational predicate p. There are no arrays in Ursala so it uses a list, and the selected item is deleted from the list and inserted into another on each iteration rather than swapped with a preceding item of the same list. <lang Ursala>

1. import std

selection_sort "p" = @iNX ~&l->rx ^(gldif ==,~&r)^/~&l ^|C/"p"\$- ~& </lang> This is already a bad way to code a sorting algorithm in this language, but with only a bit more work, we can get a bigger and slower version that more closely simulates the operations of repeatedly reordering an array. <lang Ursala> selection_sort "p" = ~&itB^?a\~&a ^|JahPfatPRC/~& ~=-~BrhPltPClhPrtPCTlrTQrS^D/"p"\$- ~& </lang> Here is a test program sorting by the partial order relation on natural numbers. <lang Ursala>

1. import nat
2. cast %nL

example = selection_sort(nleq) <294,263,240,473,596,392,621,348,220,815></lang> output:

`<220,240,263,294,348,392,473,596,621,815>`