Apply a callback to an Array
From Rosetta Code
Programming Task
This is a programming task. It lays out a problem which Rosetta Code users are encouraged to solve, using languages they know.
[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] ALGOL 68
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] C
Works with: gcc version 4.1.1
Works with: TCC version 0.9.23
Works with: ICC version 9.1
[edit] 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
[edit] 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;
}
[edit] 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] 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] 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] 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] D
U[] map(T, U)(T[] array, U delegate(T) dg) { auto result = new U[array.length]; foreach (index, element; array) result[index] = dg(element); return result; } void main() { writefln( [1, 2, 3, 4, 5].map( (int i) { return i+5; } ) ); }
Using std.algorithm:
writefln(map!("a + 5")([1, 2, 3, 4, 5]));
[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] 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] 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 = putStr.unlines.map (show.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
procedure main()
local lst
lst := [10, 20, 30, 40]
every callback(!lst)
end
procedure callback(arg)
write("->", 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
[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
Portable technique:
function map(a, func) {
for (var i in a)
a[i] = func(a[i]);
}
var a = [1, 2, 3, 4, 5];
map(a, function(v) { return v * v; });
Library: BeyondJS
With the BeyondJS library:
var a = (1).to(10).collect(Math.pow.curry(undefined,2));
With Firefox 2.0:
function cube(num) {
return Math.pow(num, 3);
}
var numbers = [1, 2, 3, 4, 5];
//get results of calling cube on every element
var cubes1 = numbers.map(cube);
//display each result in a separate dialog
cubes1.forEach(alert);
//array comprehension
var cubes2 = [cube(n) for each (n in numbers)];
var cubes3 = [n * n * n for each (n in numbers)];
Library: Functional
Functional.map('x*x*x', [1,2,3,4,5])
[edit] Logo
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 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.
[edit] Nial
each (* [first, first] ) 1 2 3 4 =1 4 9 16
[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;;
[edit] Oz
functor
import
Application System
define
Print = System.showInfo
fun{Square A}
A*A
end
fun{FuncEach Func A}
{Map A Func}
end
proc{ProcEach Proc A}
{ForAll A Proc}
end
Arr = [1 2 3 4 5]
{ProcEach Print {FuncEach Square Arr}}
{ForAll {Map Arr Square} Print} %% same
{Application.exit 0}
end
[edit] Perl
# create array
my @a = (1, 2, 3, 4, 5);
# create callback function
sub mycallback {
return 2 * shift;
}
# use array indexing
my $i;
for ($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)
[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] PL/SQL
Works with: Oracle
set serveroutput on
declare
type myarray is table of number index by binary_integer;
x myarray;
i pls_integer;
begin
-- populate array
for i in 1..5 loop
x(i) := i;
end loop;
i :=0;
-- square array
loop
i := i + 1;
begin
x(i) := x(i)*x(i);
dbms_output.put_line(x(i));
exception
when no_data_found then exit;
end;
end loop;
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] 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] 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] 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] 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] Smalltalk
#( 1 2 3 4 5 ) collect: [:n | n * n].
[edit] Tcl
If I wanted to call "myfunc" on each element of dat and dat were a list:
foreach var $dat { myfunc $var }
if dat were an array, however:
foreach name [array names dat] { myfunc $dat($name) }
[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] V
apply squaring (dup *) to each member of collection
[1 2 3 4] [dup *] map
