What are array_map(), array_reduce() and array_walk() function in PHP ?

array_map(), array_reduce(), and array_walk() are built-in PHP functions that are used to manipulate arrays.

• array_map(): This function applies a callback function to each element of an array and returns a new array with the modified elements. The syntax for array_map() is as follows:

array_map(callable $callback, array $array1 [, array $... ])

Example:

function square($n) {
  return $n * $n;
}

$numbers = [1, 2, 3, 4, 5];
$squares = array_map("square", $numbers);

print_r($squares); // Output: Array ( [0] => 1 [1] => 4 [2] => 9 [3] => 16 [4] => 25 )

• array_reduce(): This function reduces an array to a single value by applying a callback function to each element of the array. The syntax for array_reduce() is as follows:

array_reduce(array $array, callable $callback [, mixed $initial = NULL ])

Example:

function sum($carry, $item) {
  $carry += $item;
  return $carry;
}

$numbers = [1, 2, 3, 4, 5];
$total = array_reduce($numbers, "sum");

echo $total; // Output: 15

• array_walk(): This function applies a callback function to each element of an array. The syntax for array_walk() is as follows:

array_walk(array &$array, callable $callback [, mixed $userdata = NULL ])

Example:

function add_hello(&$value, $key) {
  $value = "Hello " . $value;
}

$names = ["Alice", "Bob", "Charlie"];
array_walk($names, "add_hello");

print_r($names); // Output: Array ( [0] => Hello Alice [1] => Hello Bob [2] => Hello Charlie )

Note: In array_walk(), the first parameter is passed by reference, so any changes made to the array inside the callback function will affect the original array.