array_keys
array_merge_recursive
Array Functions
PHP Manual

# array_map

(PHP 4 >= 4.0.6, PHP 5)

array_map — Applies the callback to the elements of the given arrays

### Description

array array_map ( callable `$callback` , array `$array1` [, array `$...` ] )

array_map() returns an array containing all the elements of `array1` after applying the `callback` function to each one. The number of parameters that the `callback` function accepts should match the number of arrays passed to the array_map()

### Parameters

`callback`

  Callback function to run for each element in each array.

`array1`

  An array to run through the `callback` function.

`array`

  Variable list of array arguments to run through the `callback` function.

### Return Values

Returns an array containing all the elements of `array1` after applying the `callback` function to each one.

### Examples

Example #1 array_map() example

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

This makes $b have:

    Array
    (
        [0] => 1
        [1] => 8
        [2] => 27
        [3] => 64
        [4] => 125
    )

Example #2 array_map() using a lambda function (as of PHP 5.3.0)

`<?php
$func = function($value) {
return $value * 2;
};
print_r(array_map($func, range(1, 5)));
?>`

    Array
    (
        [0] => 2
        [1] => 4
        [2] => 6
        [3] => 8
        [4] => 10
    )

Example #3 array_map() - using more arrays

`<?php
function show_Spanish($n, $m)
{
return("The number $n is called $m in Spanish");
}
function map_Spanish($n, $m)
{
return(array($n => $m));
}
$a = array(1, 2, 3, 4, 5);
$b = array("uno", "dos", "tres", "cuatro", "cinco");
$c = array_map("show_Spanish", $a, $b);
print_r($c);
$d = array_map("map_Spanish", $a , $b);
print_r($d);
?>`

The above example will output:

    // printout of $c
    Array
    (
        [0] => The number 1 is called uno in Spanish
        [1] => The number 2 is called dos in Spanish
        [2] => The number 3 is called tres in Spanish
        [3] => The number 4 is called cuatro in Spanish
        [4] => The number 5 is called cinco in Spanish
    )

    // printout of $d
    Array
    (
        [0] => Array
            (
                [1] => uno
            )

        [1] => Array
            (
                [2] => dos
            )

        [2] => Array
            (
                [3] => tres
            )

        [3] => Array
            (
                [4] => cuatro
            )

        [4] => Array
            (
                [5] => cinco
            )

    )

Usually when using two or more arrays, they should be of equal length because the callback function is applied in parallel to the corresponding elements. If the arrays are of unequal length, shorter ones will be extended with empty elements to match the length of the longest.

An interesting use of this function is to construct an array of arrays, which can be easily performed by using `NULL` as the name of the callback function

Example #4 Creating an array of arrays

`<?php
$a = array(1, 2, 3, 4, 5);
$b = array("one", "two", "three", "four", "five");
$c = array("uno", "dos", "tres", "cuatro", "cinco");
$d = array_map(null, $a, $b, $c);
print_r($d);
?>`

The above example will output:

    Array
    (
        [0] => Array
            (
                [0] => 1
                [1] => one
                [2] => uno
            )

        [1] => Array
            (
                [0] => 2
                [1] => two
                [2] => dos
            )

        [2] => Array
            (
                [0] => 3
                [1] => three
                [2] => tres
            )

        [3] => Array
            (
                [0] => 4
                [1] => four
                [2] => cuatro
            )

        [4] => Array
            (
                [0] => 5
                [1] => five
                [2] => cinco
            )

    )

If the array argument contains string keys then the returned array will contain string keys if and only if exactly one array is passed. If more than one argument is passed then the returned array always has integer keys.

Example #5 array_map() - with string keys

`<?php
$arr = array("stringkey" => "value");
function cb1($a) {
return array ($a);
}
function cb2($a, $b) {
return array ($a, $b);
}
var_dump(array_map("cb1", $arr));
var_dump(array_map("cb2", $arr, $arr));
var_dump(array_map(null, $arr));
var_dump(array_map(null, $arr, $arr));
?>`

The above example will output:

    array(1) {
      ["stringkey"]=>
      array(1) {
        [0]=>
        string(5) "value"
      }
    }
    array(1) {
      [0]=>
      array(2) {
        [0]=>
        string(5) "value"
        [1]=>
        string(5) "value"
      }
    }
    array(1) {
      ["stringkey"]=>
      string(5) "value"
    }
    array(1) {
      [0]=>
      array(2) {
        [0]=>
        string(5) "value"
        [1]=>
        string(5) "value"
      }
    }

### See Also

- array_filter() - Filters elements of an array using a callback function
- array_reduce() - Iteratively reduce the array to a single value using a callback function
- array_walk() - Apply a user function to every member of an array
- information about the callback type

array_keys
array_merge_recursive
Array Functions
PHP Manual