Using uasort() to Sort Arrays with User‑Defined Comparison Functions in PHP

The uasort() function in PHP sorts an array while keeping the association between keys and values, making it ideal for situations where the order of elements is important and a custom comparison logic is required.

Function signature :

bool uasort(array &$array, callable $cmp_function)

Description

The function takes an input array and a user‑defined comparison function. It reorders the array based on the comparison results while preserving the original keys.

Parameters array: The input array to be sorted. cmp_function: A callable that defines how two elements are compared. See usort() and uksort() for examples.

Return value

Returns TRUE on success, or FALSE on failure.

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
);

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

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
)