PHP Manual: Filters elements of an array using a callback function

Description

array array_filter(array $array, callablenull $callback = null, int $mode = 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, 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.

array_filter

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also