The usort Function

The usort function sorts an array by element values, using a callback to determine the order of elements in the sorted array. The function modifies the array itself.

The comparison function must return an integer, which depending on the comparison result: less than, equal to, or greater than zero.

Syntax

usort(array &$array, callable $callback): bool

Example

Let's sort an array in ascending order of elements:

<?php
	$arr = [1, 3, 2, 5, 4];
	
	function func($a, $b)
	{
		if ($a === $b) {
			return 0;
		} else if ($a < $b) {
			return -1;
		} else {
			return 1;
		}
	}
	
	usort($arr, 'func');
	var_dump($arr);
?>

Code execution result:

[1, 2, 3, 4, 5]

Example

Now let's sort an array in descending order of elements:

<?php
	$arr = [1, 3, 2, 5, 4];
	
	function func($a, $b)
	{
		if ($a === $b) {
			return 0;
		} else if ($a > $b) {
			return -1;
		} else {
			return 1;
		}
	}
	
	usort($arr, 'func');
	var_dump($arr);
?>

Code execution result:

[1, 2, 3, 4, 5]

Example

Now let's sort an array by ascending number of characters in the array elements:

<?php
	$arr = [
		'123',
		'1',
		'12345',
		'12',
		'1234',
	];
	
	function func($a, $b)
	{
		if (strlen($a) === strlen($b)) {
			return 0;
		} else if (strlen($a) < strlen($b)) {
			return -1;
		} else {
			return 1;
		}
	}
	
	usort($arr, 'func');
	var_dump($arr);
?>

Code execution result:

[
	'1',
	'12',
	'123',
	'1234',
	'12345',
]

The usort Function

Syntax

Example

Example

Example

See Also