array_map

Applies the callback to the elements of the given arrays

&reftitle.description; `array` `array_map` ``callable``null```callback` `array` `array` `array` `arrays`

`array_map` returns an &array; containing the results of applying the `callback` to the corresponding value of `array` (and `arrays` if more arrays are provided) used as arguments for the callback. The number of parameters that the `callback` function accepts should match the number of arrays passed to `array_map`. Excess input arrays are ignored. An `ArgumentCountError` is thrown if an insufficient number of arguments is provided.

&reftitle.parameters;

`callback`

- A `callable` to run for each element in each array.

  &null; can be passed as a value to `callback` to perform a zip operation on multiple arrays and return an array whose elements are each an array holding the elements of the input arrays of the same index (see example below). If only `array` is provided, `array_map` will return the input array.

`array`

- An array to run through the `callback` function.

`arrays`

- Supplementary variable list of array arguments to run through the `callback` function.

&reftitle.returnvalues;

Returns an array containing the results of applying the `callback` function to the corresponding value of `array` (and `arrays` if more arrays are provided) used as arguments for the callback.

The returned array will preserve the keys of the array argument if and only if exactly one array is passed. If more than one array is passed, the returned array will have sequential integer keys.

&reftitle.changelog;

&Version; | &Description;
&array.changelog.by-ref;

&reftitle.examples;

### `array_map` example

    <?php
    function cube($n)
    {
        return ($n * $n * $n);
    }

    $a = [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

    <?php
    $func = function(int $value): int {
        return $value * 2;
    };

    print_r(array_map($func, range(1, 5)));

    // Or as of PHP 7.4.0:

    print_r(array_map(fn($value): int => $value * 2, range(1, 5)));

    ?>

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

### `array_map` - using more arrays

    <?php
    function show_Spanish(int $n, string $m): string
    {
        return "The number {$n} is called {$m} in Spanish";
    }

    function map_Spanish(int $n, string $m): array
    {
        return [$n => $m];
    }

    $a = [1, 2, 3, 4, 5];
    $b = ['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

### Performing a zip operation of arrays

    <?php
    $a = [1, 2, 3, 4, 5];
    $b = ['one', 'two', 'three', 'four', 'five'];
    $c = ['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
            )

    )

### &null; `callback` with only `array`

    <?php
    $array = [1, 2, 3];
    var_dump(array_map(null, $array));
    ?>

&example.outputs;

    array(3) {
      [0]=>
      int(1)
      [1]=>
      int(2)
      [2]=>
      int(3)
    }

### `array_map` - with string keys

    <?php
    $arr = ['stringkey' => 'value'];
    function cb1($a) {
        return [$a];
    }
    function cb2($a, $b) {
        return [$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"
      }
    }

### `array_map` - associative arrays

While `array_map` does not directly support using the array key as an input, that may be simulated using `array_keys`.

    <?php
    $arr = [
        'v1' => 'First release',
        'v2' => 'Second release',
        'v3' => 'Third release',
    ];

    // Note: Before 7.4.0, use the longer syntax for anonymous functions instead.
    $callback = fn(string $k, string $v): string => "$k was the $v";

    $result = array_map($callback, array_keys($arr), array_values($arr));

    var_dump($result);
    ?>

&example.outputs;

    array(3) {
      [0]=>
      string(24) "v1 was the First release"
      [1]=>
      string(25) "v2 was the Second release"
      [2]=>
      string(24) "v3 was the Third release"
    }

&reftitle.seealso;

- `array_filter`
- `array_reduce`
- `array_walk`