array_map

Applies the callback to the elements of the given arrays

&reftitle.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`

&reftitle.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.

&reftitle.returnvalues;

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

&reftitle.examples;

### `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
    )

### `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
    )

### `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);
    ?>

&example.outputs;

    // 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

### 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);
    ?>

&example.outputs;

    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.

### `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));
    ?>

&example.outputs;

    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"
      }
    }

&reftitle.seealso;

- `array_filter`
- `array_reduce`
- `array_walk`
- &seealso.callback;