Array_map and array_walk Functions in PHP

1. Use PHP array_map() Function to Modify Elements in an Array With a User-Defined Function
2. Use array_walk() to Run an Array With a Function Including Keys in PHP

In this tutorial, we will introduce the array_map() and array_walk() functions. We will see how you can modify all elements in an array with a user-defined function.

Also, It will cover the different ways you can use the above functions.

Use PHP array_map() Function to Modify Elements in an Array With a User-Defined Function

You can use the array_map() function to send all values in an array to a user-defined function.

In the example code below, we send the values in our array $arr to the function divide and return the new values.

Example code 1:

<?php
// Define the function divide
function divide($n) {
	
	return($n/$n);
	
}
$a = array(2, 4, 6, 8, 10);

print_r(array_map("divide", $a));

?>	

Output:

Array ( [0] => 1 [1] => 1 [2] => 1 [3] => 1 [4] => 1 )

In the above code, our function divide divides all the values in the array $a by the corresponding values; hence the output 1.

Let’s try using multiple arrays.

Example code 2:

<?php
// Define the function minusAdd
function minusAdd($t, $r, $k) {
	
	return($t - $r + $k);
	
}
$arr1 = array(28, 14, 76, 38, 10);
$arr2 = array(4, 6, 20, 12, 3);
$arr3 = array(12, 6, 7 ,8 ,9);

print_r(array_map("minusAdd", $arr1, $arr2, $arr3));

?>	

Output:

Array ( [0] => 36 [1] => 14 [2] => 63 [3] => 34 [4] => 16 )

As shown in the example below, we can use the array_map() function to change the elements in an array.

Example code 3:

<?php

function synonym($s) {
	if ($s === "Male Horse") {
		return "Stallion";
	}
	return $s;
}
$arr = array("Female Horse", "Male Horse", "Pony");

print_r(array_map("synonym", $arr));

?>

Output:

Array ( [0] => Female Horse [1] => Stallion [2] => Pony )

From the above code, we change the Male Horse to Stallion with the help of the array_map function.

You can also create an array using the array_map function. For the code to work, you will have to use the null parameter in the place of the defined function.

Example code 4:

<?php

// Create an array of an array

$a1 = array('Apple', 'Eggplant', 'Cucumber', 'Mango');
$a2 = array('Fruit', 'Vegetable', 'Vegetable', 'Fruit');

$result = array_map( null, $a1, $a2);

print_r($result);

?>

Output:

Array ( [0] => Array ( [0] => Apple [1] => Fruit ) [1] => Array ( [0] => Eggplant [1] => Vegetable ) [2] => Array ( [0] => Cucumber [1] => Vegetable ) [3] => Array ( [0] => Mango [1] => Fruit ) )

Use array_walk() to Run an Array With a Function Including Keys in PHP

Since the array_map() function does not handle keys and parameters, we use array_walk() as shown in the example below.

Example code 6:

<?php

function assign($color, $key) {
	echo "The $key is $color <br>";
}
$arr = array("Apple" => "red", "Eggplant" => "purple");

array_walk($arr, "assign");

?>

Output:

The Apple is red
The Eggplant is purple