How to Use array_filter in PHP: Syntax and Examples

In PHP, array_filter is used to filter elements of an array using a callback function that returns true for elements to keep. If no callback is provided, it removes all falsy values like false, 0, or empty strings from the array.

Syntax

The array_filter function takes an array and an optional callback function. It returns a new array containing only the elements for which the callback returns true.

• array: The input array to filter.
• callback (optional): A function that receives each element and returns true to keep it or false to remove it.
• mode (optional): Controls whether to pass keys or values to the callback (default is values).

php

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

Example

This example shows how to use array_filter to keep only even numbers from an array.

php

<?php
$numbers = [1, 2, 3, 4, 5, 6];
$evenNumbers = array_filter($numbers, fn($num) => $num % 2 === 0);
print_r($evenNumbers);
?>

Output

Array
(
    [1] => 2
    [3] => 4
    [5] => 6
)

Common Pitfalls

One common mistake is expecting array_filter to reindex the filtered array. It preserves original keys, which can cause issues if you expect sequential keys.

Another pitfall is forgetting that if no callback is given, array_filter removes all falsy values like false, 0, '', and null.

php

<?php
// Wrong: expecting keys to be reindexed
$filtered = array_filter([0 => 'a', 1 => 'b', 2 => ''], fn($v) => $v !== '');
print_r($filtered);

// Right: reindex with array_values
$filtered = array_values(array_filter([0 => 'a', 1 => 'b', 2 => ''], fn($v) => $v !== ''));
print_r($filtered);
?>

Output

Array
(
    [0] => a
    [1] => b
)
Array
(
    [0] => a
    [1] => b
)

Quick Reference

Parameter	Description
array	The input array to filter
callback	Function to test each element; returns true to keep element
mode	Flag to pass keys or values to callback (default is values)

Key Takeaways

Use array_filter to keep array elements that meet a condition defined by a callback.

If no callback is given, array_filter removes all falsy values from the array.

array_filter preserves original keys; use array_values to reindex if needed.

The callback function should return true to keep an element, false to remove it.

array_filter is useful for cleaning or selecting specific data from arrays easily.