The array_filter() function in PHP is used to filter elements of an array using a callback function. It iterates over each element in the array and passes it to the callback function. If the callback returns true, the element is included in the resulting array; otherwise, it is excluded.

🔧 Syntax:

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

• $array: The input array.
• $callback (optional): A function to use for filtering. If no callback is provided, all falsey values (like false, 0, null, '', etc.) will be removed.
• $mode (optional): Can be ARRAY_FILTER_USE_KEY, ARRAY_FILTER_USE_BOTH, or 0 (default: only value is passed).

✅ Example 1: Remove falsey values from array

$data = [0, 1, false, 2, '', 3, null, 'hello'];
$result = array_filter($data);

print_r($result);

🟢 Output:

Array
(
    [1] => 1
    [3] => 2
    [5] => 3
    [7] => hello
)

By default, array_filter removes values like false, 0, '', null.

✅ Example 2: Use custom callback to filter even numbers

$numbers = [1, 2, 3, 4, 5, 6];

$result = array_filter($numbers, function($num) {
    return $num % 2 == 0;  // keep even numbers
});

print_r($result);

🟢 Output:

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

✅ Example 3: Filter associative array using keys and values

$students = [
    'john' => 75,
    'jane' => 85,
    'doe' => 50,
    'smith' => 90
];

$result = array_filter($students, function($score, $name) {
    return $score >= 80;
}, ARRAY_FILTER_USE_BOTH);

print_r($result);

🟢 Output:

Array
(
    [jane] => 85
    [smith] => 90
)

⚠️ Notes:

• The keys are preserved in the output.
• If you want to reindex the result, use array_values() on the result.