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PHP Manual

# array_filter

(PHP 4 >= 4.0.6, PHP 5)

array_filter — Filters elements of an array using a callback function

### Description

array array_filter ( array `$array` [, callable `$callback` [, int `$flag` = 0 ]] )

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.

### Parameters

`array`

  The array to iterate over

`callback`

  The callback function to use

  If no `callback` is supplied, all entries of `array` equal to `FALSE` (see converting to boolean) will be removed.

`flag`

  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

### Return Values

Returns the filtered array.

### Changelog

Version | Description
--- | ---
5.6.0 | Added optional `flag` parameter and constants `ARRAY_FILTER_USE_KEY` and `ARRAY_FILTER_USE_BOTH`

### 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 = array("a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
$array2 = array(6, 7, 8, 9, 10, 11, 12);
echo "Odd :\n";
print_r(array_filter($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
$entry = array(
0 => 'foo',
1 => false,
2 => -1,
3 => null,
4 => ''
);
print_r(array_filter($entry));
?>`

The above example will output:

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

Example #3 array_filter() with `flag`

`<?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, deleted or unset) the behavior of this function is undefined.

### See Also

- 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
- array_walk() - Apply a user supplied function to every member of an array

array_fill
array_flip
Array Functions
PHP Manual