Filters elements of an array using a callback function

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- PHP Manual
- Array Functions
- Filters elements of an array using a callback function

# array_filter

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

array_filter — Filters elements of an array using a callback function

### Description

array_filter(array `$array`, ?callable `$callback` = `null`, int `$mode` = 0): array

Iterates over each value in the `array` passing them to the `callback` function. If the `callback` function returns `true`, the current value from `array` is returned into the result array.

Array keys are preserved, and may result in gaps if the `array` was indexed. The result array can be reindexed using the array_values() function.

### Parameters

`array`

  The array to iterate over

`callback`

  The callback function to use

  If no `callback` is supplied, all empty entries of `array` will be removed. See empty() for how PHP defines empty in this case.

`mode`

  Flag determining what arguments are sent to `callback`:

  - `ARRAY_FILTER_USE_KEY` - pass key as the only argument to `callback` instead of the value
  - `ARRAY_FILTER_USE_BOTH` - pass both value and key as arguments to `callback` instead of the value
  Default is `0` which will pass value as the only argument to `callback` instead.

### Return Values

Returns the filtered array.

### Changelog

Version | Description
--- | ---
8.0.0 | `callback` is nullable now.
8.0.0 | If `callback` expects a parameter to be passed by reference, this function will now emit an `E_WARNING`.

### Examples

Example #1 array_filter() example

    <?php
    function odd($var)
    {
        // returns whether the input integer is odd
        return $var & 1;
    }

    function even($var)
    {
        // returns whether the input integer is even
        return !($var & 1);
    }

    $array1 = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
    $array2 = [6, 7, 8, 9, 10, 11, 12];

    echo "Odd :\n";
    print_r(array_filter($array1, "odd"));
    echo "Even:\n";
    print_r(array_filter($array2, "even"));
    ?>

The above example will output:

    Odd :
    Array
    (
        [a] => 1
        [c] => 3
        [e] => 5
    )
    Even:
    Array
    (
        [0] => 6
        [2] => 8
        [4] => 10
        [6] => 12
    )

Example #2 array_filter() without `callback`

    <?php

    $entry = [
        0 => 'foo',
        1 => false,
        2 => -1,
        3 => null,
        4 => '',
        5 => '0',
        6 => 0,
    ];

    print_r(array_filter($entry));
    ?>

The above example will output:

    Array
    (
        [0] => foo
        [2] => -1
    )

Example #3 array_filter() with `mode`

    <?php

    $arr = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];

    var_dump(array_filter($arr, function($k) {
        return $k == 'b';
    }, ARRAY_FILTER_USE_KEY));

    var_dump(array_filter($arr, function($v, $k) {
        return $k == 'b' || $v == 4;
    }, ARRAY_FILTER_USE_BOTH));
    ?>

The above example will output:

    array(1) {
      ["b"]=>
      int(2)
    }
    array(2) {
      ["b"]=>
      int(2)
      ["d"]=>
      int(4)
    }

### Notes

Caution

If the array is changed from the callback function (e.g. element added or unset) the behavior of this function is undefined.

### See Also

- array_intersect() - Computes the intersection of arrays
- array_find() - Returns the first element satisfying a callback function
- array_any() - Checks if at least one array element satisfies a callback function
- array_map() - Applies the callback to the elements of the given arrays
- array_reduce() - Iteratively reduce the array to a single value using a callback function