PHP array_map
Summary: in this tutorial, you will learn how to use the PHP array_map() function that creates a new array whose elements are the results of applying a callback to each element.
Introduction to the PHP array_map() function
Suppose that you have an array that holds the lengths of squares:
$lengths = [10, 20, 30];
Code language: HTML, XML (xml)
To calculate the areas of the squares, you may come up with the foreach loop like this:
$lengths = [10, 20, 30];
// calculate areas
$areas = [];
foreach ($lengths as $length) {
$areas[] = $length * $length;
}
print_r($areas);
Code language: HTML, XML (xml)
Output:
Array
(
[0] => 100
[1] => 400
[2] => 900
)Code language: PHP (php)
The foreach iterates over the elements of the $lengths array, calculates the area of each square and adds the result to the $areas array.
Alternatively, you can use the array_map() function that achieves the same result:
$lengths = [10, 20, 30];
// calculate areas
$areas = array_map(function ($length) {
return $length * $length;
}, $lengths);
print_r($areas);
Code language: HTML, XML (xml)
In this example, the array_map() applies an anonymous function to each element of the $lengths array. It returns a new array whose elements are the results of the anonymous function.
From PHP 7.4, you can use an arrow function instead of an anonymous function like this:
$lengths = [10, 20, 30];
// calculate areas
$areas = array_map(
fn ($length) => $length * $length,
$lengths
);
print_r($areas);
Code language: HTML, XML (xml)
PHP array_map() function syntax
The following shows the array_map() function syntax:
array_map ( callable|null $callback , array $array , array ...$arrays ) : arrayCode language: PHP (php)
The array_map() has the following parameters:
$callback– a callable to apply to each element in each array.$array– is an array of elements to which the callback function applies.$arrays– is a variable list of array arguments to which the callback function applies.
The array_map() function returns a new array whose elements are the result of the callback function.
This tutorial focuses on the following form of the array_map() function:
array_map ( callable $callback , array $array ) : arrayCode language: PHP (php)
PHP array_map() function examples
Let’s take some more examples of using the array_map() function.
1) Using the PHP array_map() with an array of objects
The following defines a class that has three properites: $id, $username, and $email and a list of User objects:
class User
{
public $id;
public $username;
public $email;
public function __construct(int $id, string $username, string $email)
{
$this->id = $id;
$this->username = $username;
$this->email = $email;
}
}
$users = [
new User(1, 'joe', 'joe@phptutorial.net'),
new User(2, 'john', 'john@phptutorial.net'),
new User(3, 'jane', 'jane@phptutorial.net'),
];
Code language: HTML, XML (xml)
The following illustrates how to use the array_map() function to get a list of usernames from the the $users array:
class User
{
public $id;
public $username;
public $email;
public function __construct(int $id, string $username, string $email)
{
$this->id = $id;
$this->username = $username;
$this->email = $email;
}
}
$users = [
new User(1, 'joe', 'joe@phptutorial.net'),
new User(2, 'john', 'john@phptutorial.net'),
new User(3, 'jane', 'jane@phptutorial.net'),
];
$usernames = array_map(
fn ($user) => $user->username,
$users
);
print_r($usernames);
Code language: HTML, XML (xml)
Output:
Array
(
[0] => joe
[1] => john
[2] => jane
)Code language: PHP (php)
2) Using a static method as a callback
The callback function argument of the array_map() can be a public method of a class. For example:
class Square
{
public static function area($length)
{
return $length * $length;
}
}
$lengths = [10, 20, 30];
$areas = array_map('Square::area', $lengths);
print_r($areas);
Code language: HTML, XML (xml)
How it works.
- First, define the
Squareclass that has thearea()public static method. - Second, create an array that holds the lengths of the three squares.
- Third, calculate areas of the squares based on the lengths in the
$lengthsarray using the static methodSquare::area.
Note that the syntax for passing a public static method to the array_map() function is as follows:
'className::staticMethodName'Code language: JavaScript (javascript)
And the public static method must accept the array element as an argument.
Summary
- Use the PHP
array_map()method to create a new array by applying a callback function to every element of another array.