Apply a callback to an array

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Task
Apply a callback to an array
You are encouraged to solve this task according to the task description, using any language you may know.

In this task, the goal is to take a combined set of elements and apply a function to each element.

Contents

[edit] ACL2

This example is incorrect. This is recursive list processing with a hard-coded function. First class functions are not required in this problem; "second class" functions will do (see C solution, etc). Please fix the code and remove this message.


ACL2 does not have first-class functions; this is close, however:

(defun sq-each (xs)
(if (endp xs)
nil
(cons (* (first xs) (first xs))
(sq-each (rest xs)))))

[edit] ActionScript

package
{
public class ArrayCallback
{
public function main():void
{
var nums:Array = new Array(1, 2, 3);
nums.map(function(n:Number, index:int, arr:Array):void { trace(n * n * n); });
 
// You can also pass a function reference
nums.map(cube);
}
 
private function cube(n:Number, index:int, arr:Array):void
{
trace(n * n * n);
}
}
}

[edit] Ada

Works with: GNAT version GPL 2005
with Ada.Text_Io;
with Ada.Integer_text_IO;
 
procedure Call_Back_Example is
-- Purpose: Apply a callback to an array
-- Output: Prints the squares of an integer array to the console
 
-- Define the callback procedure
procedure Display(Location : Positive; Value : Integer) is
begin
Ada.Text_Io.Put("array(");
Ada.Integer_Text_Io.Put(Item => Location, Width => 1);
Ada.Text_Io.Put(") = ");
Ada.Integer_Text_Io.Put(Item => Value * Value, Width => 1);
Ada.Text_Io.New_Line;
end Display;
 
-- Define an access type matching the signature of the callback procedure
type Call_Back_Access is access procedure(L : Positive; V : Integer);
 
-- Define an unconstrained array type
type Value_Array is array(Positive range <>) of Integer;
 
-- Define the procedure performing the callback
procedure Map(Values : Value_Array; Worker : Call_Back_Access) is
begin
for I in Values'range loop
Worker(I, Values(I));
end loop;
end Map;
 
-- Define and initialize the actual array
Sample : Value_Array := (5,4,3,2,1);
 
begin
Map(Sample, Display'access);
end Call_Back_Example;

[edit] Aime

void
map(list l, void (*fp) (object))
{
integer i;
 
i = 0;
while (i < l_length(l)) {
fp(l[i]);
i += 1;
}
}
 
 
void
out(object o)
{
o_integer(o);
o_byte(10);
}
 
 
integer
main(void)
{
list l;
 
l_append(l, 0);
l_append(l, 1);
l_append(l, 2);
l_append(l, 3);
 
map(l, out);
 
return 0;
}

[edit] ALGOL 68

Works with: ALGOL 68 version Revision 1 - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
 PROC call back proc = (INT location, INT value)VOID:
(
printf(($"array["g"] = "gl$, location, value))
);
 
PROC map = (REF[]INT array, PROC (INT,INT)VOID call back)VOID:
(
FOR i FROM LWB array TO UPB array DO
call back(i, array[i])
OD
);
 
main:
(
[4]INT array := ( 1, 4, 9, 16 );
map(array, call back proc)
)

Output:

array[         +1] =          +1
array[         +2] =          +4
array[         +3] =          +9
array[         +4] =         +16

[edit] AppleScript

on callback for arg
-- Returns a string like "arc has 3 letters"
arg & " has " & (count arg) & " letters"
end callback
 
set alist to {"arc", "be", "circle"}
repeat with aref in alist
-- Passes a reference to some item in alist
-- to callback, then speaks the return value.
say (callback for aref)
end repeat

If the callback would set arg's contents to "something", then alist would be mutated.

[edit] AutoHotkey

map("callback", "3,4,5")
 
callback(array){
Loop, Parse, array, `,
MsgBox % (2 * A_LoopField)
}
 
map(callback, array){
%callback%(array)
}

[edit] AWK

$ awk 'func psqr(x){print x,x*x}BEGIN{split("1 2 3 4 5",a);for(i in a)psqr(a[i])}'
4 16
5 25
1 1
2 4
3 9

[edit] Babel

We can alter the list in place:

((main 
{ (1 1 2 3 5 8 13 21) dup
{double !} each
{%d ' ' . <<} each})
 
(double { dup 2 * set }))

Or, we can leave the original list unmodified:

((main 
{ (1 1 2 3 5 8 13 21)
{double !} each
collect !
{%d ' ' . <<} each})
 
(double { 2 * })
 
(collect { -1 take }))

Both versions produce the same output:

2 2 4 6 10 16 26 42 

Because lists and arrays are distinct in Babel, we can also do a similar procedure over an array, with the same results as above:

((main 
{ [val 1 1 2 3 5 8 13 21]
{double !} eachar
collect !
{%d ' ' . <<} each})
 
(double { 2 * })
 
(collect { -1 take }))

[edit] BBC BASIC

      DIM a(4)
a() = 1, 2, 3, 4, 5
PROCmap(a(), FNsqrt())
FOR i = 0 TO 4
PRINT a(i)
NEXT
END
 
DEF FNsqrt(n) = SQR(n)
 
DEF PROCmap(array(), RETURN func%)
LOCAL I%
FOR I% = 0 TO DIM(array(),1)
array(I%) = FN(^func%)(array(I%))
NEXT
ENDPROC
 

Produces this output:

         1
1.41421356
1.73205081
         2
2.23606798

[edit] Bracmat

( ( callbackFunction1
= location value
.  !arg:(?location,?value)
& out$(str$(array[ !location "] = " !!value))
)
& ( callbackFunction2
= location value
.  !arg:(?location,?value)
& !!value^2:?!value
)
& ( map
= arr len callback i
.  !arg:(?arr,?len,?callback)
& 0:?i
& whl
' ( !i:<!len
& !callback$(!i,!i$!arr)
& 1+!i:?i
)
)
& tbl$(array,4)
& 1:?(0$array)
& 2:?(1$array)
& 3:?(2$array)
& 4:?(3$array)
& map$(array,4,callbackFunction1)
& map$(array,4,callbackFunction2)
& map$(array,4,callbackFunction1)
);

Output:

array[0] = 1
array[1] = 2
array[2] = 3
array[3] = 4
array[0] = 1
array[1] = 4
array[2] = 9
array[3] = 16

[edit] Brat

#Print out each element in array
[:a :b :c :d :e].each { element |
p element
}

Alternatively:

[:a :b :c :d :e].each ->p

[edit] C

callback.h

#ifndef CALLBACK_H
#define CALLBACK_H
 
/*
* By declaring the function in a separate file, we allow
* it to be used by other source files.
*
* It also stops ICC from complaining.
*
* If you don't want to use it outside of callback.c, this
* file can be removed, provided the static keyword is prepended
* to the definition.
*/

void map(int* array, int len, void(*callback)(int,int));
 
#endif

callback.c

#include <stdio.h>
#include "callback.h"
 
/*
* We don't need this function outside of this file, so
* we declare it static.
*/

static void callbackFunction(int location, int value)
{
printf("array[%d] = %d\n", location, value);
}
 
void map(int* array, int len, void(*callback)(int,int))
{
int i;
for(i = 0; i < len; i++)
{
callback(i, array[i]);
}
}
 
int main()
{
int array[] = { 1, 2, 3, 4 };
map(array, 4, callbackFunction);
return 0;
}

Output

 array[0] = 1
 array[1] = 2
 array[2] = 3
 array[3] = 4

[edit] C#

Works with: C# version 2.0+
Works with: Visual C# version 2005
using System; 
 
static class Program
{
// Purpose: Apply a callback (or anonymous method) to an Array
// Output: Prints the squares of an int array to the console.
// Compiler: Visual Studio 2005
// Framework: .net 2
 
[STAThread]
public static void Main()
{
int[] intArray = { 1, 2, 3, 4, 5 };
 
// Using a callback,
Console.WriteLine("Printing squares using a callback:");
Array.ForEach<int>(intArray, PrintSquare);
 
// or using an anonymous method:
Console.WriteLine("Printing squares using an anonymous method:");
Array.ForEach<int>
(
intArray,
delegate(int value)
{
Console.WriteLine(value * value);
});
}
 
public static void PrintSquare(int value)
{
Console.WriteLine(value * value);
}
}
Works with: C# version 3.0+

This version uses the C# 3 lambda notation.

int[] intArray = { 1, 2, 3, 4, 5 };
Array.ForEach(intArray, i => Console.WriteLine(i * i));

[edit] C++

Works with: g++ version 4.1.1

[edit] C-Style Array

#include <iostream> //cout for printing
#include <algorithm> //for_each defined here
 
//create the function (print the square)
void print_square(int i) {
std::cout << i*i << " ";
}
 
int main() {
//create the array
int ary[]={1,2,3,4,5};
//stl for_each
std::for_each(ary,ary+5,print_square);
return 0;
}
//prints 1 4 9 16 25

[edit] std::vector

Library: STL
#include <iostream>  // cout for printing
#include <algorithm> // for_each defined here
#include <vector> // stl vector class
 
// create the function (print the square)
void print_square(int i) {
std::cout << i*i << " ";
}
 
int main() {
// create the array
std::vector<int> ary;
ary.push_back(1);
ary.push_back(2);
ary.push_back(3);
ary.push_back(4);
ary.push_back(5);
// stl for_each
std::for_each(ary.begin(),ary.end(),print_square);
return 0;
}
//prints 1 4 9 16 25

More tricky with binary function

#include <iostream>   // cout for printing
#include <algorithm> // for_each defined here
#include <vector> // stl vector class
#include <functional> // bind and ptr_fun
 
// create a binary function (print any two arguments together)
template<class type1,class type2>
void print_juxtaposed(type1 x, type2 y) {
std::cout << x << y;
}
 
int main() {
// create the array
std::vector<int> ary;
ary.push_back(1);
ary.push_back(2);
ary.push_back(3);
ary.push_back(4);
ary.push_back(5);
// stl for_each, using binder and adaptable unary function
std::for_each(ary.begin(),ary.end(),std::bind2nd(std::ptr_fun(print_juxtaposed<int,std::string>),"x "));
return 0;
}
//prints 1x 2x 3x 4x 5x

[edit] Boost.Lambda

Library: Boost
using namespace std;
using namespace boost::lambda;
vector<int> ary(10);
int i = 0;
for_each(ary.begin(), ary.end(), _1 = ++var(i)); // init array
transform(ary.begin(), ary.end(), ostream_iterator<int>(cout, " "), _1 * _1); // square and output

[edit] C++11

#include <vector>
#include <iostream>
#include <algorithm>
#include <iterator>
 
int main() {
std::vector<int> intVec(10);
std::iota(std::begin(intVec), std::end(intVec), 1 ); // Fill the vector
std::transform(std::begin(intVec) , std::end(intVec), std::begin(intVec),
[](int i) { return i * i ; } ); // Transform it with closures
std::copy(std::begin(intVec), end(intVec) ,
std::ostream_iterator<int>(std::cout, " "));
std::cout << std::endl;
return 0;
}

[edit] Clean

Define a function and an initial (unboxed) array.

square x = x * x
 
values :: {#Int}
values = {x \\ x <- [1 .. 10]}

One can easily define a map for arrays, which is overloaded and works for all kinds of arrays (lazy, strict, unboxed).

mapArray f array = {f x \\ x <-: array}

Apply the function to the initial array (using a comprehension) and print result.

Start :: {#Int}
Start = mapArray square values

[edit] Clojure

;; apply a named function, inc
(map inc [1 2 3 4])
;; apply a function
(map (fn [x] (* x x)) [1 2 3 4])
;; shortcut syntax for a function
(map #(* % %) [1 2 3 4])

[edit] COBOL

Basic implementation of a map function:

       IDENTIFICATION DIVISION.
PROGRAM-ID. Map.
 
DATA DIVISION.
WORKING-STORAGE SECTION.
01 Table-Size CONSTANT 30.
 
LOCAL-STORAGE SECTION.
01 I USAGE UNSIGNED-INT.
 
LINKAGE SECTION.
01 Table-Param.
03 Table-Values USAGE COMP-2 OCCURS Table-Size TIMES.
 
01 Func-Id PIC X(30).
 
PROCEDURE DIVISION USING Table-Param Func-Id.
PERFORM VARYING I FROM 1 BY 1 UNTIL Table-Size < I
CALL Func-Id USING BY REFERENCE Table-Values (I)
END-PERFORM
 
GOBACK
.

[edit] CoffeeScript

 
map = (arr, f) -> (f(e) for e in arr)
arr = [1, 2, 3, 4, 5]
f = (x) -> x * x
console.log map arr, f # prints [1, 4, 9, 16, 25]
 


[edit] Common Lisp

Imperative: print 1, 2, 3, 4 and 5:

(map nil #'print #(1 2 3 4 5))

Functional: collect squares into new vector that is returned:

(defun square (x) (* x x))
(map 'vector #'square #(1 2 3 4 5))

Destructive, like the Javascript example; add 1 to every slot of vector *a*:

(defvar *a* (vector 1 2 3))
(map-into *a* #'1+ *a*)

[edit] Component Pascal

BlackBox Component Builder

 
MODULE Callback;
IMPORT StdLog;
 
TYPE
Callback = PROCEDURE (x: INTEGER;OUT doubled: INTEGER);
Callback2 = PROCEDURE (x: INTEGER): INTEGER;
 
PROCEDURE Apply(proc: Callback; VAR x: ARRAY OF INTEGER);
VAR
i: INTEGER;
BEGIN
FOR i := 0 TO LEN(x) - 1 DO;
proc(x[i],x[i]);
END
END Apply;
 
PROCEDURE Apply2(func: Callback2; VAR x: ARRAY OF INTEGER);
VAR
i: INTEGER;
BEGIN
FOR i := 0 TO LEN(x) - 1 DO;
x[i] := func(x[i]);
END
END Apply2;
 
PROCEDURE Double(x: INTEGER; OUT y: INTEGER);
BEGIN
y := x * x;
END Double;
 
PROCEDURE Double2(x: INTEGER): INTEGER;
BEGIN
RETURN x * x
END Double2;
 
PROCEDURE Do*;
VAR
i: INTEGER;
ary: ARRAY 10 OF INTEGER;
 
 
BEGIN
FOR i := 0 TO LEN(ary) - 1 DO ary[i] := i END;
Apply(Double,ary);
FOR i := 0 TO LEN(ary) - 1 DO
StdLog.Int(ary[i]);StdLog.Ln
END;
StdLog.Ln;
Apply2(Double2,ary);
FOR i := 0 TO LEN(ary) - 1 DO
StdLog.Int(ary[i]);StdLog.Ln
END
END Do;
END Callback.
 

Execute: ^Q Callback.Do
Output:

 0
 1
 4
 9
 16
 25
 36
 49
 64
 81

 0
 1
 16
 81
 256
 625
 1296
 2401
 4096
 6561

[edit] D

import std.stdio, std.algorithm;
 
void main() {
auto items = [1, 2, 3, 4, 5];
auto m = items.map!(x => x + 5)();
writeln(m);
}
Output:
[6, 7, 8, 9, 10]

[edit] Delphi

 
// Declare the callback function
procedure callback(const AInt:Integer);
begin
WriteLn(AInt);
end;
 
const
// Declare a static array
myArray:Array[0..4] of Integer=(1,4,6,8,7);
var
// Declare interator variable
i:Integer;
begin
// Iterate the array and apply callback
for i:=0 to length(myArray)-1 do
callback(myArray[i]);
end.
 

[edit] Déjà Vu

There is a map builtin that does just this.

!. map @++ [ 1 4 8 ]
 
#implemented roughly like this:
#map f lst:
# ]
# for i in lst:
# f i
# [
Output:
[ 2 5 9 ]

[edit] E

def array := [1,2,3,4,5]
def square(value) {
return value * value
}

Example of builtin iteration:

def callback(index, value) { 
println(`Item $index is $value.`)
}
array.iterate(callback)

There is no built-in map function yet. The following is one of the ways one could be implemented, returning a plain list (which is usually an array in implementation).

def map(func, collection) {
def output := [].diverge()
for item in collection {
output.push(func(item))
}
return output.snapshot()
}
println(map(square, array))

[edit] Efene

square = fn (N) {
N * N
}
 
# list comprehension
squares1 = fn (Numbers) {
[square(N) for N in Numbers]
}
 
# functional form
squares2a = fn (Numbers) {
lists.map(fn square:1, Numbers)
}
 
# functional form with lambda
squares2b = fn (Numbers) {
lists.map(fn (N) { N * N }, Numbers)
}
 
# no need for a function
squares3 = fn (Numbers) {
[N * N for N in Numbers]
}
 
@public
run = fn () {
Numbers = [1, 3, 5, 7]
io.format("squares1 : ~p~n", [squares1(Numbers)])
io.format("squares2a: ~p~n", [squares2a(Numbers)])
io.format("squares2b: ~p~n", [squares2b(Numbers)])
io.format("squares3 : ~p~n", [squares3(Numbers)])
}
 

[edit] EGL

delegate callback( i int ) returns( int ) end
 
program ApplyCallbackToArray
function main()
values int[] = [ 1, 2, 3, 4, 5 ];
 
func callback = square;
for ( i int to values.getSize() )
values[ i ] = func( values[ i ] );
end
 
for ( i int to values.getSize() )
SysLib.writeStdout( values[ i ] );
end
end
 
function square( i int ) returns( int )
return( i * i );
end
end

[edit] Elena

#define system.
 
#symbol PrintSecondPower =
(:n) [ console writeLine:(n * n) ].
 
#symbol program =
[
#var anArray := (1, 2, 3, 4, 5, 6, 7, 8, 9, 10).
 
control foreach:anArray &do:PrintSecondPower.
].

[edit] Erlang

A list would be more commonly used in Erlang rather than an array.

 
1> L = [1,2,3].
[1,2,3]
 

You can use lists:foreach/2 if you just want to apply the callback to each element of the list.

 
2> lists:foreach(fun(X) -> io:format("~w ",[X]) end, L).
1 2 3 ok
 

Or you can use lists:map/2 if you want to create a new list with the result of the callback on each element.

 
3> lists:map(fun(X) -> X + 1 end, L).
[2,3,4]
 

Or you can use lists:foldl/3 if you want to accumulate the result of the callback on each element into one value.

 
4> lists:foldl(fun(X, Sum) -> X + Sum end, 0, L).
6
 

[edit] Euphoria

function apply_to_all(sequence s, integer f)
-- apply a function to all elements of a sequence
sequence result
result = {}
for i = 1 to length(s) do
-- we can call add1() here although it comes later in the program
result = append(result, call_func(f, {s[i]}))
end for
return result
end function
 
function add1(atom x)
return x + 1
end function
 
-- add1() is visible here, so we can ask for its routine id
? apply_to_all({1, 2, 3}, routine_id("add1"))
-- displays {2,3,4}

This is also "Example 2" in the Euphoria documentation for routine_id(). Note that this example will not work for multi-dimensional sequences.

[edit] Factor

Print each element squared:

{ 1 2 3 4 } [ sq . ] each

Collect return values:

{ 1 2 3 4 } [ sq ] map

[edit] Fantom

In Fantom, functions can be passed to a collection iterator, such as 'each'. 'map' is used similarly, and the results are collected into a list.

 
class Main
{
public static Void main ()
{
[1,2,3,4,5].each |Int i| { echo (i) }
Int[] result := [1,2,3,4,5].map |Int i->Int| { return i * i }
echo (result)
}
}
 

Output:

1
2
3
4
5
[1, 4, 9, 16, 25]

[edit] FBSL

User-defined mapping function:

#APPTYPE CONSOLE
 
FOREACH DIM e IN MyMap(Add42, {1, 2, 3})
PRINT e, " ";
NEXT
 
PAUSE
 
FUNCTION MyMap(f, a)
DIM ret[]
FOREACH DIM e IN a
ret[] = f(e)
NEXT
RETURN ret
END FUNCTION
 
FUNCTION Add42(n): RETURN n + 42: END FUNCTION

Output:

43 44 45
Press any key to continue...

Standard MAP() function:

#APPTYPE CONSOLE
 
DIM languages[] = {{"English", {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"}}, _
{"French", {"un", "deux", "trois", "quatre", "cinq", "six", "sept", "huit", "neuf", "dix"}}}
 
MAP(SpeakALanguage, languages)
 
PAUSE
 
SUB NameANumber(lang, nb, number)
PRINT "The number ", nb, " is called ", STRENC(number), " in ", lang
END SUB
 
SUB SpeakALanguage(lang)
MAP(NameANumber, lang[0], 1 TO 10, lang[1])
PRINT LPAD("", 40, "-")
END SUB

Output:

The number 1 is called "one" in English
The number 2 is called "two" in English
The number 3 is called "three" in English
The number 4 is called "four" in English
The number 5 is called "five" in English
The number 6 is called "six" in English
The number 7 is called "seven" in English
The number 8 is called "eight" in English
The number 9 is called "nine" in English
The number 10 is called "ten" in English
----------------------------------------
The number 1 is called "un" in French
The number 2 is called "deux" in French
The number 3 is called "trois" in French
The number 4 is called "quatre" in French
The number 5 is called "cinq" in French
The number 6 is called "six" in French
The number 7 is called "sept" in French
The number 8 is called "huit" in French
The number 9 is called "neuf" in French
The number 10 is called "dix" in French
----------------------------------------
Press any key to continue...

[edit] Forth

This is a word that will call a given function on each cell in an array.

: map ( addr n fn -- )
-rot cells bounds do i @ over execute i ! cell +loop ;

Example usage:

create data 1 , 2 , 3 , 4 , 5 ,
data 5 ' 1+ map \ adds one to each element of data

[edit] Fortran

Elemental functions.

Works with: Fortran version ISO 95 and later
module arrCallback
contains
elemental function cube( x )
implicit none
real :: cube
real, intent(in) :: x
cube = x * x * x
end function cube
end module arrCallback
program testAC
use arrCallback
implicit none
integer :: i, j
real, dimension(3,4) :: b, &
a = reshape( (/ ((10 * i + j, i = 1, 3), j = 1, 4) /), (/ 3,4 /) )
 
do i = 1, 3
write(*,*) a(i,:)
end do
 
b = cube( a ) ! Applies CUBE to every member of a,
! and stores each result in the equivalent element of b
do i = 1, 3
write(*,*) b(i,:)
end do
end program testAC
Works with: ANSI FORTRAN version 77 (with MIL-STD-1753 structured DO) and later
      program test
C
C-- Declare array:
integer a(5)
C
C-- Fill it with Data
data a /45,22,67,87,98/
C
C-- Do something with all elements (in this case: print their squares)
do i=1,5
print *,a(i)*a(i)
end do
C
end

[edit] FP

{square * . [id, id]}
& square: <1,2,3,4,5>

[edit] Frink

 
f = {|x| x^2} // Anonymous function to square input
a = [1,2,3,5,7]
println[map[f, a]]
 

[edit] F#

Apply a named function to each member of the array. The result is a new array of the same size as the input.

let evenp x = x % 2 = 0
let result = Array.map evenp [| 1; 2; 3; 4; 5; 6 |]

The same can be done using anonymous functions, this time squaring the members of the input array.

let result = Array.map (fun x -> x * x) [|1; 2; 3; 4; 5|]

Use iter if the applied function does not return a value.

Array.iter (fun x -> printfn "%d" x) [|1; 2; 3; 4; 5|]

[edit] FunL

[1, 2, 3].foreach( println )
 
[1, 2, 3].foreach( a -> println(2a) )
Output:
1
2
3
2
4
6

[edit] GAP

a := [1 .. 4];
b := ShallowCopy(a);
 
# Apply and replace values
Apply(a, n -> n*n);
a;
# [ 1, 4, 9, 16 ]
 
# Apply and don't change values
List(b, n -> n*n);
# [ 1, 4, 9, 16 ]
 
# Apply and don't return anything (only side effects)
Perform(b, Display);
1
2
3
4
 
b;
# [ 1 .. 4 ]

[edit] Go

Translation of: Ruby

The task was originally written with a Ruby example, so here are Go versions of the current Ruby examples.

Perhaps in contrast to Ruby, it is idiomatic in Go to use the for statement:

package main
 
import "fmt"
 
func main() {
for _, i := range []int{1, 2, 3, 4, 5} {
fmt.Println(i * i)
}
}

Alternatively though, an array-like type can be defined and callback-style methods can be defined on it to apply a function to the elements.

package main
 
import "fmt"
 
type intSlice []int
 
func (s intSlice) each(f func(int)) {
for _, i := range s {
f(i)
}
}
 
func (s intSlice) Map(f func(int) int) intSlice {
r := make(intSlice, len(s))
for j, i := range s {
r[j] = f(i)
}
return r
}
 
func main() {
s := intSlice{1, 2, 3, 4, 5}
 
s.each(func(i int) {
fmt.Println(i * i)
})
 
fmt.Println(s.Map(func(i int) int {
return i * i
}))
}
Output:
1
4
9
16
25
[1 4 9 16 25]

[edit] Groovy

Print each value in a list

[1,2,3,4].each { println it }

Create a new list containing the squares of another list

[1,2,3,4].collect { it * it }

[edit] Haskell

[edit] List

Works with: GHC
let square x = x*x
let values = [1..10]
map square values

Using list comprehension to generate a list of the squared values

[square x | x <- values]

Using function composition to create a function that will print the squares of a list

let printSquares = mapM_ (print.square)
printSquares values

[edit] Array

Works with: GHC
import Data.Array.IArray
let square x = x*x
let values = array (1,10) [(i,i)|i <- [1..10]] :: Array Int Int
amap square values

[edit] Icon and Unicon

procedure main()
local lst
lst := [10, 20, 30, 40]
every callback(write,!lst)
end
 
procedure callback(p,arg)
return p(" -> ", arg)
end

[edit] IDL

Hard to come up with an example that isn't completely contrived. IDL doesn't really distinguish between a scalar and an array; thus

b = a^3

will yield a scalar if a is scalar or a vector if a is a vector or an n-dimensional array if a is an n-dimensional array

[edit] Io

list(1,2,3,4,5) map(squared)

[edit] J

Solution:

   "_1

Example:

   callback =:  *:
array =: 1 2 3 4 5
 
callback"_1 array
1 4 9 16 25

But note that this is a trivial example since *: 1 2 3 4 5 would get the same result. Then again, this is something of a trivial exercise in J since all of J is designed around the idea of applying functions usefully to arrays.

[edit] Java

As of the current version of Java, you have to define an interface for each type of function you want to use. The next version of Java will introduce function types.

So if you want to perform an action (which doesn't return anything) on an array of int's:

interface IntToVoid {
void run(int x);
}
 
for (int z : myIntArray) {
new IntToVoid() {
public void run(int x) {
System.out.println(x);
}
}.run(z);
}

Or if you want to perform "map" - return an array of the results of function applications:

interface IntToInt {
int run(int x);
}
 
int[] result = new int[myIntArray.length];
for (int i = 0; i < myIntArray.length; i++) {
result[i] =
new IntToInt() {
public int run(int x) {
return x * x;
}
}.run(myIntArray[i]);
}

[edit] JavaScript

[edit] ES3

function map(a, func) {
var ret = [];
for (var i = 0; i < a.length; i++) {
ret[i] = func(a[i]);
}
return ret;
}
 
map([1, 2, 3, 4, 5], function(v) { return v * v; });

[edit] ES5

[1, 2, 3, 4, 5].map(function(v) { return v * v; });

[edit] ES6

[1, 2, 3, 4, 5].map(v => v * v);

The result is always:

[1, 4, 9, 16, 25]

[edit] Joy

[1 2 3 4 5] [dup *] map.

[edit] jq

# Illustration of map/1 using the builtin filter: exp
map(exp) # exponentiate each item in the input list
 
# A compound expression can be specified as the argument to map, e.g.
map( (. * .) + sqrt ) # x*x + sqrt(x)
 
# The compound expression can also be a composition of filters, e.g.
map( sqrt|floor ) # the floor of the sqrt
 
# Array comprehension
reduce .[] as $n ([]; . + [ exp ])
 
# Elementwise operation
[.[] + 1 ] # add 1 to each element of the input array
 
Here is a transcript illustrating how the last of these jq expressions can be evaluated:
$ jq -c ' [.[] + 1 ]'
[0, 1 , 10]
[1,2,11]

[edit] Julia

 
numbers = [1, 3, 5, 7]
 
square1 = [square(n) for n in numbers] # list comprehension
 
squares2a = map(square, numbers) # functional form
 
squares2b = map(x -> x*x, numbers) # functional form with `lambda`
 
#There is also extended block form for the map function
squares2c = map(numbers) do x
sum = 0
for i = 1:x
sum += x^2 #trivial, but you get the point
end
return sum
end
 
squares3 = [n * n for n in numbers] # no need for a function,
 
squares4 = numbers .* numbers # element-wise operation
 
squares4a = numbers .^ 2 # most arithmetic operations can be done element-wise

[edit] Lang5

: square(*)  dup * ;
[1 2 3 4 5] square . "\n" .
[1 2 3 4 5] 'square apply . "\n" .

[edit] Lasso

define cube(n::integer) => #n*#n*#n
 
local(
mynumbers = array(1, 2, 3, 4, 5),
mycube = array
)
 
#mynumbers -> foreach => {
#mycube -> insert(cube(#1))
}
 
#mycube

-> array(1, 8, 27, 64, 125)

[edit] Lisaac

+ a : ARRAY(INTEGER);
+ b : {INTEGER;};
 
a := ARRAY(INTEGER).create 1 to 3;
1.to 3 do { i : INTEGER;
a.put i to i;
};
 
b := { arg : INTEGER;
(arg * arg).print;
'\n'.print;
};
 
a.foreach b;

[edit]

to square :x
output :x * :x
end
show map "square [1 2 3 4 5]  ; [1 4 9 16 25]
show map [? * ?] [1 2 3 4 5]  ; [1 4 9 16 25]
foreach [1 2 3 4 5] [print square ?]  ; 1 4 9 16 25, one per line

[edit] Lua

Say we have an array:

myArray = {1, 2, 3, 4, 5}

A map function for this would be

map = function(f, data)
local result = {}
for k,v in ipairs(data) do
result[k] = f(v)
end
return result
end

Together with our array and a square function this yields:

myFunc = function(x) return x*x end
 
print(unpack( map(myFunc, myArray) ))
--> 1 4 9 16 25

If you used pairs() instead of ipairs(), this would even work on a hash table in general. However, remember that hash table do not have an implicit ordering on their elements, like arrays do, so pairs() is not guaranteed to return the elements in the same order as ipairs()

[edit] M4

define(`foreach', `pushdef(`$1')_foreach($@)popdef(`$1')')dnl
define(`_arg1', `$1')dnl
define(`_foreach', `ifelse(`$2', `()', `',
`define(`$1', _arg1$2)$3`'$0(`$1', (shift$2), `$3')')')dnl
dnl
define(`apply',`foreach(`x',$1,`$2(x)')')dnl
dnl
define(`z',`eval(`$1*2') ')dnl
apply(`(1,2,3)',`z')

Output:

2 4 6

[edit] Maple

For lists and sets, which in Maple are immutable, a new object is returned. Either the built-in procedure map, or the short syntax of a trailing tilde (~) on the applied operator may be used.

 
> map( sqrt, [ 1.1, 3.2, 5.7 ] );
[1.048808848, 1.788854382, 2.387467277]
 
> map( x -> x + 1, { 1, 3, 5 } );
{2, 4, 6}
 
> sqrt~( [ 1.1, 3.2, 5.7 ] );
[1.048808848, 1.788854382, 2.387467277]
 
> (x -> x + 1)~( { 1, 3, 5 } );
{2, 4, 6}
 

For Arrays (Vectors, Matrices, etc.) both map and trailing tilde also work, and by default create a new object, leaving the input Array unchanged.

 
> a := Array( [ 1.1, 3.2, 5.7 ] );
a := [1.1, 3.2, 5.7]
 
> sqrt~( a );
[1.048808848, 1.788854382, 2.387467277]
 
> a;
[1.1, 3.2, 5.7]
 
> map( sqrt, a );
[1.048808848, 1.788854382, 2.387467277]
 
> a;
[1.1, 3.2, 5.7]
 

However, since these are mutable data structures in Maple, it is possible to use map to modify its input according to the applied procedure.

 
> map[inplace]( sqrt, a );
[1.048808848, 1.788854382, 2.387467277]
 
> a;
[1.048808848, 1.788854382, 2.387467277]
 

The Array a has been modified.

It is also possible to pass additional arguments to the mapped procedure.

 
> map( `+`, [ 1, 2, 3 ], 3 );
[4, 5, 6]
 

Passing additional arguments *before* the arguments from the mapped data structure is achieved using map2, or the more general map[n] procedure.

 
> map2( `-`, 5, [ 1, 2, 3 ] );
[4, 3, 2]
 
> map[2]( `/`, 5, [ 1, 2, 3 ] );
[5, 5/2, 5/3]
 

[edit] Mathematica

(#*#)& /@ {1, 2, 3, 4}
 
Map[Function[#*#], {1, 2, 3, 4}]
 
Map[((#*#)&,{1,2,3,4}]
 
Map[Function[w,w*w],{1,2,3,4}]

[edit] MATLAB

There are two types of arrays in MATLAB: arrays and cell arrays. MATLAB includes two functions, one for each of these data types, that accomplish the specification for this task. For arrays, we use "arrayfun()"; for cell arrays we use "cellfun()".
Example: For both of these function the first argument is a function handle for the function we would like to apply to each element. The second argument is the array whose elements are modified by the function. The function can be any function, including user defined functions.

>> array = [1 2 3 4 5]
 
array =
 
1 2 3 4 5
 
>> arrayfun(@sin,array)
 
ans =
 
Columns 1 through 4
 
0.841470984807897 0.909297426825682 0.141120008059867 -0.756802495307928
 
Column 5
 
-0.958924274663138
 
>> cellarray = {1,2,3,4,5}
 
cellarray =
 
[1] [2] [3] [4] [5]
 
>> cellfun(@tan,cellarray)
 
ans =
 
Columns 1 through 4
 
1.557407724654902 -2.185039863261519 -0.142546543074278 1.157821282349578
 
Column 5
 
-3.380515006246586

[edit] Maxima

/* for lists or sets */
 
map(sin, [1, 2, 3, 4]);
map(sin, {1, 2, 3, 4});
 
/* for matrices */
 
matrixmap(sin, matrix([1, 2], [2, 4]));

[edit] Modula-3

MODULE Callback EXPORTS Main;
 
IMPORT IO, Fmt;
 
TYPE CallBack = PROCEDURE (a: CARDINAL; b: INTEGER);
Values = REF ARRAY OF INTEGER;
 
VAR sample := ARRAY [1..5] OF INTEGER {5, 4, 3, 2, 1};
callback := Display;
 
PROCEDURE Display(loc: CARDINAL; val: INTEGER) =
BEGIN
IO.Put("array[" & Fmt.Int(loc) & "] = " & Fmt.Int(val * val) & "\n");
END Display;
 
PROCEDURE Map(VAR values: ARRAY OF INTEGER; size: CARDINAL; worker: CallBack) =
VAR lvalues := NEW(Values, size);
BEGIN
FOR i := FIRST(lvalues^) TO LAST(lvalues^) DO
worker(i, values[i]);
END;
END Map;
 
BEGIN
Map(sample, NUMBER(sample), callback);
END Callback.

[edit] Nemerle

The Nemerle.Collections namespace defines the methods Iter() (if the function applied is void) and Map() (if the function applied returns a value).

def seg = array[1, 2, 3, 5, 8, 13];
def squares = seq.Map(x => x*x);

[edit] NewLISP

> (map (fn (x) (* x x)) '(1 2 3 4))
(1 4 9 16)
 

[edit] Nial

each (* [first, first] ) 1 2 3 4
=1 4 9 16

[edit] Nimrod

var arr = [1,2,3,4]
arr.map proc(some: var int) = echo(some, " squared = ", some*some)
Output:
 1 squared = 1
 2 squared = 4
 3 squared = 9
 4 squared = 16

[edit] Objeck

 
use Structure;
 
bundle Default {
class Test {
function : Main(args : String[]) ~ Nil {
Run();
}
 
function : native : Run() ~ Nil {
values := IntVector->New([1, 2, 3, 4, 5]);
squares := values->Apply(Square(Int) ~ Int);
each(i : squares) {
squares->Get(i)->PrintLine();
};
}
 
function : Square(value : Int) ~ Int {
return value * value;
}
}
}
 

[edit] OCaml

This function is part of the standard library:

Array.map

Usage example:

let square x = x * x;;
let values = Array.init 10 ((+) 1);;
Array.map square values;;

Or with lists (which are more typical in OCaml):

let values = [1;2;3;4;5;6;7;8;9;10];;
List.map square values;;

Use iter if the applied function does not return a value.

Array.iter (fun x -> Printf.printf "%d" x) [|1; 2; 3; 4; 5|];;
List.iter (fun x -> Printf.printf "%d" x) [1; 2; 3; 4; 5];;

with partial application we can also write:

Array.iter (Printf.printf "%d") [|1; 2; 3; 4; 5|];;
List.iter (Printf.printf "%d") [1; 2; 3; 4; 5];;

[edit] Octave

Almost all the built-in can operate on each element of a vector or matrix; e.g. sin([pi/2, pi, 2*pi]) computes the function sin on pi/2, pi and 2*pi (returning a vector). If a function does not accept vectors/matrices as arguments, the arrayfun can be used.

function e = f(x, y)
e = x^2 + exp(-1/(y+1));
endfunction
 
% f([2,3], [1,4]) gives and error, but
arrayfun(@f, [2, 3], [1,4])
% works

(The function f can be rewritten so that it can accept vectors as argument simply changing operators to their dot relatives: e = x.^2 + exp(-1 ./ (y.+1)))

[edit] ooRexx

ooRexx doesn't directly support callbacks on array items, but this is pretty easy to implement using Routine objects.

 
start = .array~of("Rick", "Mike", "David", "Mark")
new = map(start, .routines~reversit)
call map new, .routines~sayit
 
 
-- a function to perform an iterated callback over an array
-- using the provided function. Returns an array containing
-- each function result
::routine map
use strict arg array, function
resultArray = .array~new(array~items)
do item over array
resultArray~append(function~call(item))
end
return resultArray
 
::routine reversit
use arg string
return string~reverse
 
::routine sayit
use arg string
say string
return .true -- called as a function, so a result is required
 
 

[edit] Order

Both sequences and tuples support the usual map operation seen in many functional languages. Sequences also support 8seq_for_each, and a few variations, which returns 8nil.

#include <order/interpreter.h>
 
ORDER_PP( 8tuple_map(8fn(8X, 8times(8X, 8X)), 8tuple(1, 2, 3, 4, 5)) )
// -> (1,4,9,16,25)
 
ORDER_PP( 8seq_map(8fn(8X, 8times(8X, 8X)), 8seq(1, 2, 3, 4, 5)) )
// -> (1)(4)(9)(16)(25)
 
ORDER_PP( 8seq_for_each(8fn(8X, 8print(8X 8comma)), 8seq(1, 2, 3, 4, 5)) )
// prints 1,2,3,4,5, and returns 8nil

[edit] Oz

declare
fun{Square A}
A*A
end
 
Lst = [1 2 3 4 5]
 
%% apply a PROCEDURE to every element
{ForAll Lst Show}
 
%% apply a FUNCTION to every element
Result = {Map Lst Square}
{Show Result}

[edit] PARI/GP

Works with: PARI/GP version 2.4.2 and above
callback(n)=n+n;
apply(callback, [1,2,3,4,5])

[edit] Pascal

See Delphi

[edit] Perl

# create array
my @a = (1, 2, 3, 4, 5);
 
# create callback function
sub mycallback {
return 2 * shift;
}
 
# use array indexing
for (my $i = 0; $i < scalar @a; $i++) {
print "mycallback($a[$i]) = ", mycallback($a[$i]), "\n";
}
 
# using foreach
foreach my $x (@a) {
print "mycallback($x) = ", mycallback($x), "\n";
}
 
# using map (useful for transforming an array)
my @b = map mycallback($_), @a; # @b is now (2, 4, 6, 8, 10)
 
# and the same using an anonymous function
my @c = map { $_ * 2 } @a; # @c is now (2, 4, 6, 8, 10)
 
# use a callback stored in a variable
my $func = \&mycallback;
my @d = map $func->($_), @a; # @d is now (2, 4, 6, 8, 10)
 
# filter an array
my @e = grep { $_ % 2 == 0 } @a; # @e is now (2, 4)

[edit] Perl 6

Works with: Rakudo version #21 "Seattle"
my $function = { 2 * $^x + 3 };
my @array = 1 .. 5;
 
# via map function
.say for map $function, @array;
 
# via map method
.say for @array.map($function);
 
# via for loop
for @array {
say $function($_);
}
 
# via the "hyper" metaoperator and method indirection
say @array».$function;

[edit] PHP

function cube($n)
{
return($n * $n * $n);
}
 
$a = array(1, 2, 3, 4, 5);
$b = array_map("cube", $a);
print_r($b);

[edit] PicoLisp

: (mapc println (1 2 3 4 5))  # Print numbers
1
2
3
4
5
-> 5
 
: (mapcar '((N) (* N N)) (1 2 3 4 5)) # Calculate squares
-> (1 4 9 16 25)
 
: (mapcar ** (1 2 3 4 5) (2 .)) # Same, using a circular list
-> (1 4 9 16 25)
 
: (mapcar if '(T NIL T NIL) '(1 2 3 4) '(5 6 7 8)) # Conditional function
-> (1 6 3 8)

[edit] Pike

int cube(int n)
{
return n*n*n;
}
 
array(int) a = ({ 1,2,3,4,5 });
array(int) b = cube(a[*]); // automap operator
array(int) c = map(a, cube); // conventional map function

[edit] PL/I

   declare x(5) initial (1,3,5,7,8);
x = sqrt(x);
x = sin(x);

[edit] PL/SQL

PL/SQL doesn't have callbacks, though we can pass around an object and use its method to simulate one. Further, this callback method can be defined in an abstract class that the mapping function will expect.

-- Let's create a generic class with one method to be used as an interface:
CREATE OR REPLACE
TYPE callback AS OBJECT (
-- A class needs at least one member even though we don't use it
-- There's no generic OBJECT type, so let's call it NUMBER
dummy NUMBER,
-- Here's our function, and since PL/SQL doesn't have generics,
-- let's use type NUMBER for our params
MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER
) NOT FINAL NOT instantiable;
/
 
-- Now let's inherit from that, defining a class with one method. We'll have ours square a number.
-- We can pass this class into any function that takes type callback:
CREATE OR REPLACE TYPE CB_SQUARE under callback (
OVERRIDING MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER
)
/
CREATE OR REPLACE
TYPE BODY CB_SQUARE AS
OVERRIDING MEMBER FUNCTION exec(n NUMBER) RETURN NUMBER IS
BEGIN
RETURN n * n;
END exec;
END;
/
 
-- And a package to hold our test
CREATE OR REPLACE
PACKAGE PKG_CALLBACK AS
myCallback cb_square;
TYPE intTable IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;
ints intTable;
i PLS_INTEGER;
 
PROCEDURE test_callback;
END PKG_CALLBACK;
/
 
CREATE OR REPLACE PACKAGE BODY PKG_CALLBACK AS
-- Our generic mapping function that takes a "method" and a collection
-- Note that it takes the generic callback type
-- that doesn't know anything about squaring
PROCEDURE do_callback(myCallback IN callback, ints IN OUT intTable) IS
i PLS_INTEGER;
myInt NUMBER;
BEGIN
FOR i IN 1 .. ints.COUNT LOOP
myInt := ints(i);
-- PL/SQL call's the child's method
ints(i) := myCallback.exec(myInt);
END LOOP;
END do_callback;
 
PROCEDURE test_callback IS
BEGIN
myCallback := cb_square(NULL);
FOR i IN 1..5 LOOP
ints(i) := i;
END LOOP;
 
do_callback(myCallback, ints);
 
i := ints.FIRST;
WHILE i IS NOT NULL LOOP
DBMS_OUTPUT.put_line(ints(i));
i := ints.next(i);
END LOOP;
END test_callback;
END PKG_CALLBACK;
/
 
BEGIN
PKG_CALLBACK.TEST_CALLBACK();
END;
/

[edit] Pop11

;;; Define a procedure
define proc(x);
printf(x*x, '%p,');
enddefine;
 
;;; Create array
lvars ar = { 1 2 3 4 5};
 
;;; Apply procedure to array
appdata(ar, proc);

If one wants to create a new array consisting of transformed values then procedure mapdata may be more convenient.

[edit] PostScript

The forall operator applies a procedure to each element of an array, a packed array or a string.

[1 2 3 4 5] { dup mul = } forall

In this case the respective square numbers for the elements are printed.

To create a new array from the results above code can simply be wrapped in []:

[ [1 2 3 4 5] { dup mul } forall ]
Library: initlib
 
[1 2 3 4 5] {dup *} map
 

[edit] PowerShell

This can be done in PowerShell with the ForEach-Object cmdlet which applies a scriptblock to each element of an array:

1..5 | ForEach-Object { $_ * $_ }

To recreate a map function, found in other languages the same method applies:

function map ([array] $a, [scriptblock] $s) {
$a | ForEach-Object $s
}

[edit] Prolog

Prolog doesn't have arrays, but we can do it with lists. This can be done in the console mode.

 ?- assert((fun(X, Y) :- Y is 2 * X)).
true.
 
?- maplist(fun, [1,2,3,4,5], L).
L = [2,4,6,8,10].
 

[edit] PureBasic

Procedure Cube(Array param.i(1))
Protected n.i
For n = 0 To ArraySize(param())
Debug Str(param(n)) + "^3 = " + Str(param(n) * param(n) * param(n))
Next
EndProcedure
 
Dim AnArray.i(4)
 
For n = 0 To ArraySize(AnArray())
AnArray(n) = Random(99)
Next
 
Cube(AnArray())

[edit] Python

def square(n):
return n * n
 
numbers = [1, 3, 5, 7]
 
squares1 = [square(n) for n in numbers] # list comprehension
 
squares2a = map(square, numbers) # functional form
 
squares2b = map(lambda x: x*x, numbers) # functional form with `lambda`
 
squares3 = [n * n for n in numbers] # no need for a function,
# anonymous or otherwise
 
isquares1 = (n * n for n in numbers) # iterator, lazy
 
import itertools
isquares2 = itertools.imap(square, numbers) # iterator, lazy

To print squares of integers in the range from 0 to 9, type:

print " ".join(str(n * n) for n in range(10))

Or:

print " ".join(map(str, map(square, range(10))))

Result:

0 1 4 9 16 25 36 49 64 81

[edit] R

Many functions can take advantage of implicit vectorisation, e.g.

cube <- function(x) x*x*x
elements <- 1:5
cubes <- cube(elements)

Explicit looping over array elements is also possible.

cubes <- numeric(5)
for(i in seq_along(cubes))
{
cubes[i] <- cube(elements[i])
}

Loop syntax can often simplified using the *apply family of functions.

elements2 <- list(1,2,3,4,5)
cubes <- sapply(elements2, cube)

In each case above, the value of 'cubes' is

1   8  27  64 125

[edit] Racket

 
#lang racket
 
;; using the `for/vector' comprehension form
(for/vector ([i #(1 2 3 4 5)]) (sqr i))
 
;; the usual functional `map'
(vector-map sqr #(1 2 3 4 5))
 

[edit] Raven

# To print the squared elements
[1 2 3 4 5] each dup * print
# To obtain a new array
group [1 2 3 4 5] each
dup *
list

[edit] REBOL

rebol [
Title: "Array Callback"
Date: 2010-01-04
Author: oofoe
URL: http://rosettacode.org/wiki/Apply_a_callback_to_an_Array
]

 
map: func [
"Apply a function across an array."
f [native! function!] "Function to apply to each element of array."
a [block!] "Array to process."
/local x
][x: copy [] forall a [append x do [f a/1]] x]
 
square: func [x][x * x]
 
; Tests:
 
assert: func [code][print [either do code [" ok"]["FAIL"] mold code]]
 
print "Simple loop, modify in place:"
assert [[1 100 81] = (a: [1 10 9] forall a [a/1: square a/1] a)]
 
print [crlf "Functional style with 'map':"]
assert [[4 16 36] = map :square [2 4 6]]
 
print [crlf "Applying native function with 'map':"]
assert [[2 4 6] = map :square-root [4 16 36]]

Output:

Simple loop, modify in place:
  ok [[1 100 81] = (a: [1 100 81] forall a [a/1: square a/1] a)]

Functional style with 'map':
  ok [[4 16 36] = map :square [2 4 6]]

Applying native function with 'map':
  ok [[2 4 6] = map :square-root [4 16 36]]

[edit] Retro

Using the array' library to multiply each value in an array by 10 and display the results:

[ 1 2 3 4 5 ] ^array'fromQuote [ 10 * ] ^array'map ^array'display

Retro also provides ^array'apply for use when you don't want to alter the contents of the array:

[ "Hello" "World" "Foo" ] ^array'fromQuote [ "%s " puts ] ^array'apply

[edit] REXX

/*REXX program to apply a  callback  to a  stemmed  (REXX)  array.      */
a.=; b.=
a.0= 0
a.1= 1
a.2= 2
a.3= 3
a.4= 4
a.5= 5
a.6= 6
a.7= 7
a.8= 8
a.9= 9
a.10=10
 
call listab 'before'
call bangit 'a','b' /*factorialize the A array, store results in B */
call listab ' after'
exit /*stick a fork in it, we're done.*/
/*──────────────────────────────────BANGIT subroutine───────────────────*/
bangit: do i=0
_=value(arg(1)'.'i); if _=='' then return
call value arg(2)'.'i,fact(_)
end /*i*/
/*──────────────────────────────────FACT subroutine─────────────────────*/
fact: procedure; !=1; do j=2 to arg(1); !=!*j; end; return !
/*──────────────────────────────────LISTAB subroutine───────────────────*/
listab: do j=0 while a.j\==''; say arg(1) 'a.'j"="a.j; end /*j*/
say; do k=0 while b.k\==''; say arg(1) 'b.'k"="b.k; end /*k*/
return

output

before a.0=0
before a.1=1
before a.2=2
before a.3=3
before a.4=4
before a.5=5
before a.6=6
before a.7=7
before a.8=8
before a.9=9
before a.10=10

 after a.0=0
 after a.1=1
 after a.2=2
 after a.3=3
 after a.4=4
 after a.5=5
 after a.6=6
 after a.7=7
 after a.8=8
 after a.9=9
 after a.10=10

 after b.0=1
 after b.1=1
 after b.2=2
 after b.3=6
 after b.4=24
 after b.5=120
 after b.6=720
 after b.7=5040
 after b.8=40320
 after b.9=362880
 after b.10=3628800

[edit] RLaB

RLaB has two type of arrays: 'standard' or 1-dimensional, that can be a row- or a column-vectory; and, 'associative' which are called lists. For standard array its entry identifier (index) is an integer in range 1:N where N is the size of the array. For associative array its entry identifier is a string consisting of printable ASCII characters.

All scalar mathematical functions are 'matrix-optimized' meaning that if the argument to a function is a matrix, then the return value of the function is a matrix of the same size as the input argument, where the function is applied to the individual entries of the matrix. Consider an example:

 
>> x = rand(2,4)
0.707213207 0.275298961 0.396757763 0.232312312
0.215619868 0.207078017 0.565700032 0.666090571
>> sin(x)
0.649717845 0.271834652 0.386430003 0.230228332
0.213952984 0.205601224 0.536006923 0.617916954
 

This can be done on entry-by-entry basis, but one has to keep in mind that the 'for' or 'while' loops are slow in interpreted languages, and RLaB is no exception.

 
x = rand(2,4);
y = zeros(2,4);
for (i in 1:2)
{
for (j in 1:4)
{
y[i;j] = sin( x[i;j] );
}
}
 


The functions can take lists as arguments, but then it has to be specified within the body of the function what to do with the list elements. Given a list call it 'x' there is a RLaB function 'members' which returns a string vector with the names of the elements of the list.

 
x = <<>>;
for (i in 1:9)
{
x.[i] = rand();
}
 
y = <<>>;
for (i in members(x))
{
y.[i] = sin( x.[i] );
}
 

[edit] Ruby

You could use a traditional "for i in arr" approach like below:

for i in [1,2,3,4,5] do
puts i**2
end

Or you could the more preferred ruby way of an iterator (which is borrowed from SmallTalk)

[1,2,3,4,5].each{ |i| puts i**2 }

To create a new array of each value squared

[1,2,3,4,5].map{ |i| i**2 }

[edit] Salmon

These examples apply the square function to a list of the numbers from 0 through 9 to produce a new list of their squares, then iterate over the resulting list and print the squares.

function apply(list, ageless to_apply)
(comprehend(x; list) (to_apply(x)));
 
function square(x) (x*x);
 
iterate(x; apply([0...9], square))
x!;

With short identifiers:

include "short.salm";
 
fun apply(list, ageless to_apply)
(comp(x; list) (to_apply(x)));
 
fun square(x) (x*x);
 
iter(x; apply([0...9], square))
x!;

With the numbers given as a list of individual elements:

function apply(list, to_apply)
(comprehend(x; list) (to_apply(x)));
 
function square(x) (x*x);
 
iterate(x; apply([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], square))
x!;

[edit] Sather

class MAIN is
do_something(i:INT):INT is
return i * i;
end;
 
main is
a:ARRAY{INT} := |1, 2, 3, 4, 5|;
-- we use an anonymous closure to apply our do_something "callback"
a.map(bind(do_something(_)));
loop #OUT + a.elt! + "\n"; end;
end;
end;

[edit] Scala

val l = List(1,2,3,4)
l.foreach {i => println(i)}

When the argument appears only once -as here, i appears only one in println(i) - it may be shortened to

l.foreach(println(_))

Same for an array

val a = Array(1,2,3,4)
a.foreach {i => println(i)}
a.foreach(println(_)) '' // same as previous line''

Or for an externally defined function:

def doSomething(in: int) = {println("Doing something with "+in)}
l.foreach(doSomething)

There is also a for syntax, which is internally rewritten to call foreach. A foreach method must be defined on a

for(val i <- a) println(i)

It is also possible to apply a function on each item of an list to get a new list (same on array and most collections)

val squares = l.map{i => i * i} ''//squares is''  List(1,4,9,16)

Or the equivalent for syntax, with the additional keyword yield, map is called instead of foreach

val squares = for (val i <- l) yield i * i

[edit] Scheme

(define (square n) (* n n))
(define x #(1 2 3 4 5))
(map square (vector->list x))

A single-line variation

(map (lambda (n) (* n n)) '(1 2 3 4 5))

For completeness, the map function (which is R5RS standard) can be coded as follows:

(define (map f L)
(if (null? L)
L
(cons (f (car L)) (map f (cdr L)))))

[edit] Sidef

Define a callback function:

func callback(i) { say i**2 };

Now, the function will get called for each element:

[1,2,3,4].each(callback);

Same as above, but with the function inlined:

[1,2,3,4].each{|i| say i**2 };

To create a new array of each value squared, we can use:

[1,2,3,4,5].map{|i| i**2 };

[edit] Slate

#( 1 2 3 4 5 ) collect: [| :n | n * n].

[edit] Smalltalk

#( 1 2 3 4 5 ) collect: [:n | n * n].

[edit] Sparkling

The foreach function calls the supplied callback on each element of the (possibly associative) array, passing it each key and the corresponding value:

let numbers = { 1, 2, 3, 4 };
foreach(numbers, function(idx, num) {
print(num);
});

The map function applies the transform to each key-value pair and constructs a new array, of which the keys are the keys of the original array, and the corresponding values are the return values of each call to the transform function:

let dict = { "foo": 42, "bar": 13, "baz": 37 };
let doubled = map(dict, function(key, val) {
return val * 2;
});

[edit] Standard ML

 
map f l
 

i.e.

 
map (fn x=>x+1) [1,2,3];; (* [2,3,4] *)
 

[edit] SuperCollider

Actually, there is a builtin squared operator:

[1, 2, 3].squared;  // returns [1, 4, 9]

Anything that is a Collection can be used with collect:

[1, 2, 3].collect({ arg x; x*x });

List comprehension combined with a higher-order function can also be used:

var square = {
arg x;
x*x;
};
var map = {
arg fn, xs;
all {: fn.value(x), x <- xs };
};
map.value(square,[1,2,3]);

[edit] Swift

func square(n: Int) -> Int {
return n * n
}
 
let numbers = [1, 3, 5, 7]
 
let squares1a = numbers.map(square) // map method on array
 
let squares1b = numbers.map {x in x*x} // map method on array with anonymous function
 
let squares2a = map(numbers, square) // map function
 
let squares2b = map(numbers) {x in x*x} // map function with anonymous function
 
let isquares1 = lazy(numbers).map(square) // lazy sequence

[edit] Tcl

If I wanted to call "myfunc" on each element of dat and dat were a list:

foreach var $dat {
myfunc $var
}

This does not retain any of the values returned by myfunc.

if dat were an (associative) array, however:

foreach name [array names dat] {
myfunc $dat($name)
}

More functional, with a simple map function:

proc map {f list} {
set res {}
foreach e $list {lappend res [$f $e]}
return $res
}
proc square x {expr {$x*$x}}
 
% map square {1 2 3 4 5}
1 4 9 16 25

[edit] TI-89 BASIC

© For no return value
Define foreach(fe_cname,fe_list) = Prgm
Local fe_i
For fe_i,1,dim(fe_list)
#fe_cname(fe_list[fe_i])
EndFor
EndPrgm
 
© For a list of results
Define map(map_cnam,map_list) = seq(#map_cnam(map_list[map_i]),map_i,1,dim(map_list))
 
Define callback(elem) = Prgm
Disp elem
EndPrgm
 
foreach("callback", {1,2,3,4,5})
Disp map("√", {1,2,3,4,5})

Output:

1
2
3
4
5
\begin{Bmatrix}1 & \sqrt{2} & \sqrt{3} & 2 & \sqrt{5}\end{Bmatrix}

[edit] TIScript

JavaScript alike:

var a = [1, 2, 3, 4, 5];
a.map(function(v) { return v * v; })
 

Using short form of lambda notation:

var a = [1, 2, 3, 4, 5];
a.map( :v: v*v );
 

[edit] Toka

( array count function -- )
{
value| array fn |
[ i array ] is I
[ to fn swap to array 0 swap [ I array.get :stack fn invoke I array.put ] countedLoop ]
} is map-array
 
( Build an array )
5 cells is-array a
10 0 a array.put
11 1 a array.put
12 2 a array.put
13 3 a array.put
14 4 a array.put
 
( Add 1 to each item in the array )
a 5 [ 1 + ] map-array

[edit] TorqueScript

--Elm 03:41, 18 June 2012 (UTC)

Callbacks:

 
function map(%array,%arrayCount,%function)
{
for(%i=0;%i<%arrayCount;%i++)
{
eval("%a = "@%array@"["@%i@"];");
eval(""@%function@"("@%a@");");
}
}
 

Now to set up an array:

 
$array[0] = "Hello.";
$array[1] = "Hi.";
$array[2] = "How are you?";
 

Now to call the function correctly:

 
map("$array",3,"echo");
 

Which should result in:

 
=> Hello.
 
=> Hi.
 
=> How are you?
 

[edit] TXR

Print 1 through 10 out of a vector, using prinl the callback, right from the system shell command prompt:

$ txr -e '[mapdo prinl #(1 2 3 4 5 6 7 8 9 10)]'
1
2
3
4
5
6
7
8
9
10

mapdo is like mapcar but doesn't accumulate a list, suitable for imperative programming situations when the function is invoked to perform a side effect.

TXR extends Lisp list processing primitives to work with vectors and strings also, which is why mapdo cheerfully traverses a vector.

[edit] UNIX Shell

Works with: Bourne Shell
map() {
map_command=$1
shift
for i do "$map_command" "$i"; done
}
list=1:2:3
(IFS=:; map echo $list)
Works with: ksh93
Works with: pdksh
Works with: zsh
map() {
typeset command=$1
shift
for i do "$command" "$i"; done
}
set -A ary 1 2 3
map print "${ary[@]}"
Works with: zsh
map(){for i ($*[2,-1]) $1 $i}
a=(1 2 3)
map print $a

[edit] Ursala

The * is a built-in map operator. This example shows a map of the successor function over a list of natural numbers.

#import nat
 
#cast %nL
 
demo = successor* <325,32,67,1,3,7,315>

output:

<326,33,68,2,4,8,316>

[edit] V

apply squaring (dup *) to each member of collection

[1 2 3 4] [dup *] map

[edit] VBScript

I really have my doubts as to whether this really counts as a callback. I used the same thing in the solution to Amb.

[edit] Implementation
 
class callback
dim sRule
 
public property let rule( x )
sRule = x
end property
 
public default function applyTo(a)
dim p1
for i = lbound( a ) to ubound( a )
p1 = a( i )
a( i ) = eval( sRule )
next
applyTo = a
end function
end class
 
[edit] Invocation
 
dim a1
dim cb
set cb = new callback
 
cb.rule = "ucase(p1)"
a1 = split("my dog has fleas", " " )
cb.applyTo a1
wscript.echo join( a1, " " )
 
cb.rule = "p1 ^ p1"
a1 = array(1,2,3,4,5,6,7,8,9,10)
cb.applyto a1
wscript.echo join( a1, ", " )
 
 
[edit] Output
MY DOG HAS FLEAS
1, 4, 27, 256, 3125, 46656, 823543, 16777216, 387420489, 10000000000

[edit] Vim Script

map() works with lists and dictionaries. The second argument is an expression string where v:val is replaced by the current value and v:key by the current key (for lists the key is the index). The result of evaluating the string will be the new value. The list/dictionary is modified in place.

echo map([10, 20, 30], 'v:val * v:val')
echo map([10, 20, 30], '"Element " . v:key . " = " . v:val')
echo map({"a": "foo", "b": "Bar", "c": "BaZ"}, 'toupper(v:val)')
echo map({"a": "foo", "b": "Bar", "c": "BaZ"}, 'toupper(v:key)')
Output:
[100, 400, 900]                                                                 
['Element 0 = 10', 'Element 1 = 20', 'Element 2 = 30']                          
{'a': 'FOO', 'b': 'BAR', 'c': 'BAZ'}                                            
{'a': 'A', 'b': 'B', 'c': 'C'}

[edit] Vorpal

Given and array, A, and a function, F, mapping F over the elements of A is simple:

A.map(F)

If F takes 2 arguments, x and , then simply pass them to map. They will be passed to F when as it is applied to each element of A.

A.map(F, x, y)

[edit] Wart

map prn '(1 2 3 4 5)

Output:

1
2
3
4
5

[edit] zkl

L(1,2,3,4,5).apply('+(5))

Output:

L(6,7,8,9,10)
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