PHP array_filter Function

last modified March 13, 2025

The PHP array_filter function filters elements of an array using a callback function. It returns a new array containing all elements that pass the callback test.

Basic Definition

The array_filter function iterates over each array element and passes it to the callback. Elements that return true are included in the result array.

Syntax: array_filter(array $array, ?callable $callback = null, int $mode = 0): array. The callback can be omitted to filter empty values. Mode controls arguments passed to callback.

Basic array_filter Example

This example filters out all odd numbers from an array, keeping only evens.

basic_array_filter.php

<?php

$numbers = [1, 2, 3, 4, 5, 6];
$evenNumbers = array_filter($numbers, function($n) {
    return $n % 2 === 0;
});

print_r($evenNumbers);

The callback checks if each number is even. The resulting array contains only elements where the callback returned true. Note original keys are preserved.

Filtering Without Callback

When no callback is provided, array_filter removes all falsy values from the array.

no_callback.php

<?php

$mixedValues = [0, 1, '', 'hello', null, false, true, [], [1]];
$filtered = array_filter($mixedValues);

print_r($filtered);

This removes 0, empty string, null, false, and empty array - all falsy values. Only truthy values remain in the filtered array.

Filtering with ARRAY_FILTER_USE_BOTH

Using the mode parameter, we can pass both value and key to the callback.

use_both.php

<?php

$data = [
    'user1' => 'admin',
    'user2' => 'editor',
    'user3' => 'viewer',
    'user4' => 'admin'
];

$admins = array_filter($data, function($value, $key) {
    return $value === 'admin' && $key !== 'user1';
}, ARRAY_FILTER_USE_BOTH);

print_r($admins);

This filters for admin users while excluding user1. The callback receives both value and key, allowing complex filtering logic based on both.

Filtering Array of Objects

array_filter works well with object arrays when filtering based on object properties.

object_filter.php

<?php

class Product {
    public function __construct(
        public string $name,
        public float $price,
        public bool $inStock
    ) {}
}

$products = [
    new Product('Laptop', 999.99, true),
    new Product('Phone', 699.99, false),
    new Product('Tablet', 399.99, true)
];

$availableProducts = array_filter($products, fn($p) => $p->inStock);

print_r($availableProducts);

This filters out products not in stock. The arrow function checks the inStock property, keeping only available products in the result.

Filtering with ARRAY_FILTER_USE_KEY

When we need to filter based on array keys rather than values.

use_key.php

<?php

$config = [
    'db_host' => 'localhost',
    'db_user' => 'root',
    'db_pass' => 'secret',
    'cache_ttl' => 3600,
    'debug_mode' => true
];

$dbConfig = array_filter($config, function($key) {
    return str_starts_with($key, 'db_');
}, ARRAY_FILTER_USE_KEY);

print_r($dbConfig);

This filters the array to include only keys starting with 'db_'. The callback receives only the key when using ARRAY_FILTER_USE_KEY mode.

Best Practices

Preserve Keys: Remember array_filter keeps original keys by default.
Type Safety: Add type hints in callbacks for better code.
Performance: For large arrays, consider more efficient approaches.
Readability: Use named functions for complex filtering logic.
Reindexing: Use array_values() if you need sequential keys.

Source

PHP array_filter Documentation

This tutorial covered the PHP array_filter function with practical examples showing its usage for various array filtering scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

List all PHP Array Functions.

Ebooks