How to filter PHP arrays using array_filter() function? Explain the basic usage in detail

M66 2025-05-14

In PHP development, arrays are very commonly used data structures. When operating arrays, we often need to filter the array, such as removing null values, retaining elements that meet certain conditions, etc. The array_filter() function is a very practical tool designed specifically for this.

This article will explain in detail the basic usage of array_filter() , the meaning of parameters and some common usage scenarios, to help you quickly master the practical application of this function.

1. Introduction to array_filter() function

array_filter() is one of the built-in functions of PHP. Its purpose is to use a callback function to filter each element in the array, leaving only elements with the return value true . Its syntax is as follows:

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

Parameter description:

$array : The original array to filter.
$callback (optional): A callback function used to determine whether an element is retained. If null , the default removal values are false , null , empty string '' , number 0 , empty array [] and other "false values".
$mode (PHP 7.4+): Specifies whether the content passed to the callback function is a value, key, or key-value pair.

2. Basic usage examples

1. Remove "false values" from array

This is the most common way to use it, suitable for cleaning form data or configuration items, etc.:

$data = ["apple", "", null, 0, "banana", false];

$filtered = array_filter($data);

print_r($filtered);

Output result:

Array
(
    [0] => apple
    [4] => banana
)

When no callback function is passed, array_filter() will remove "false value" by default.

2. Use callback functions to customize filtering logic

For example, we only keep strings with length greater than 5 in the array:

$words = ["apple", "strawberry", "banana", "kiwi"];

$filtered = array_filter($words, function($word) {
    return strlen($word) > 5;
});

print_r($filtered);

Output:

Array
(
    [1] => strawberry
    [2] => banana
)

3. Filter by key name (using ARRAY_FILTER_USE_KEY)

Starting from PHP 7.4, you can control the filtering content through the third parameter $mode :

$data = [
    'a' => 100,
    'b' => 200,
    'x' => 300,
];

$filtered = array_filter($data, function($key) {
    return $key === 'x';
}, ARRAY_FILTER_USE_KEY);

print_r($filtered);

Output:

Array
(
    [x] => 300
)

3. Array_filter() Common application scenarios

1. Clean the form data

$_POST = [
    'username' => 'alice',
    'email' => '',
    'age' => null,
];

$clean_data = array_filter($_POST);

This can quickly remove null fields and only valid data is retained.

2. Filter user data that meets certain criteria

$users = [
    ['name' => 'Tom', 'active' => true],
    ['name' => 'Jerry', 'active' => false],
    ['name' => 'Spike', 'active' => true],
];

$active_users = array_filter($users, function($user) {
    return $user['active'];
});

print_r($active_users);

3. Dynamically filter legal links in URL list

$urls = [
    'https://m66.net/home',
    'invalid-url',
    'http://m66.net/contact',
    '',
];

$valid_urls = array_filter($urls, function($url) {
    return filter_var($url, FILTER_VALIDATE_URL);
});

print_r($valid_urls);

4. Things to note

After using array_filter() , the key name of the original array will not be reset (if you need to reset it, you can use it with array_values() ).
If you need to filter by keyname, make sure PHP version >= 7.4 and use ARRAY_FILTER_USE_KEY .
The callback function should return true or false to determine whether the element is retained.

Related Tags:
array_filter