Master PHP Array Functions: array_filter, array_map, array_walk & array_reduce

array_filter()

The array_filter() function iterates over an array and keeps only the elements for which the supplied callback returns a truthy value. Keys are preserved by default. If no callback is provided, all values that evaluate to true are retained. An optional third argument ( ARRAY_FILTER_USE_KEY or ARRAY_FILTER_USE_BOTH) can be used to pass the key or both key and value to the callback.

$arr = ['a', 0, 'b', 'c', 1, 2, 3, 4, 5, 6, 7];
// Keep only string values
$new_arr = array_filter($arr, function ($v) {
    return is_string($v);
});
print_r($new_arr);
// Output:
// Array ( [0] => a [2] => b [3] => c )

array_map()

array_map()

applies a callback to each element of one or more arrays and returns a new array containing the results. The callback receives the corresponding values from each input array in the order they are passed. If the arrays have different lengths, array_map() stops at the shortest one.

$arr1 = [1, 2, 3, 4, 5];
$arr2 = [6, 7, 8, 9, 10, 55];
$new_arr = array_map(function ($val1, $val2) {
    return $val1 + $val2;
}, $arr1, $arr2);
var_dump($new_arr);
// Output:
// array(6) {
//   [0]=> int(7)
//   [1]=> int(9)
//   [2]=> int(11)
//   [3]=> int(13)
//   [4]=> int(15)
//   [5]=> int(55)
// }

array_walk()

array_walk()

traverses an array and invokes a user‑defined callback for each element. The callback receives the value and the key; the value can be modified by reference, allowing in‑place changes to the original array.

$arr = ['a', 0, 'b', 'c', 1, 2, 3, 4, 5, 6, 7];
array_walk($arr, function (&$val, $key) {
    // Append the string "_x" to each element for demonstration
    $val = $val . '_x';
});
var_dump($arr);
// Example output (truncated):
// array(11) {
//   [0]=> string(3) "a_x"
//   [1]=> string(2) "0_x"
//   ...
// }

array_reduce()

array_reduce()

collapses an array to a single scalar value by repeatedly applying a callback. The callback receives the accumulator (carry) and the current item, and must return the updated accumulator. An optional third argument supplies the initial value of the accumulator.

$array = [10, 15, 20, 60];
$sum = array_reduce($array, function ($carry, $item) {
    return $carry + $item;
}, 50); // start with 50
print_r('Total: ' . $sum);
// Output: Total: 155

// Equivalent built‑in function
print_r(array_sum($array)); // 105

These built‑in array functions enable developers to replace explicit for / foreach loops with concise, functional‑style code, often improving readability and performance.