ArrayObject::uasort

(PHP 5 >= 5.2.0, PHP 7, PHP 8)

ArrayObject::uasort — Sort the entries with a user-defined comparison function and maintain key association

Description

public ArrayObject::uasort(callable $callback): true

This function sorts the entries such that keys maintain their correlation with the entry that they are associated with, using a user-defined comparison function.

This is used mainly when sorting associative arrays where the actual element order is significant.

Note:

If two members compare as equal, they retain their original order. Prior to PHP 8.0.0, their relative order in the sorted array was undefined.

Parameters

callback

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

callback(mixed $a, mixed $b): int
Caution

Returning non-integer values from the comparison function, such as float, will result in an internal cast to int of the callback's return value. So values such as 0.99 and 0.1 will both be cast to an integer value of 0, which will compare such values as equal.

Return Values

Always returns true.

Changelog

Version Description
8.2.0 The return type is true now; previously, it was bool.

Examples

Example #1 ArrayObject::uasort() example

<?php
// Comparison function
function cmp($a, $b) {
if ($a == $b) {
return 0;
}
return ($a < $b) ? -1 : 1;
}

// Array to be sorted
$array = array('a' => 4, 'b' => 8, 'c' => -1, 'd' => -9, 'e' => 2, 'f' => 5, 'g' => 3, 'h' => -4);
$arrayObject = new ArrayObject($array);
print_r($arrayObject);

// Sort and print the resulting array
$arrayObject->uasort('cmp');
print_r($arrayObject);
?>

The above example will output:

Array
(
    [a] => 4
    [b] => 8
    [c] => -1
    [d] => -9
    [e] => 2
    [f] => 5
    [g] => 3
    [h] => -4
)
Array
(
    [d] => -9
    [h] => -4
    [c] => -1
    [e] => 2
    [g] => 3
    [a] => 4
    [f] => 5
    [b] => 8
)

See Also