PHP uksort() Function: Sorting Array Keys with a User‑Defined Comparison Callback

The uksort() function in PHP sorts an array by its keys using a user‑provided comparison callback, allowing custom ordering criteria.

Signature: bool uksort(array &$array, callable $cmp_function) .

Parameters: $array – the input array; $cmp_function – a callable that must return an integer less than, equal to, or greater than zero when the first argument is respectively less than, equal to, or greater than the second.

Return value: TRUE on success, FALSE on failure.

Example:

<?php
function cmp($a, $b) {
    $a = preg_replace('@^(a|an|the) @', '', $a);
    $b = preg_replace('@^(a|an|the) @', '', $b);
    return strcasecmp($a, $b);
}

$a = array(
    "John"   => 1,
    "the Earth" => 2,
    "an apple"  => 3,
    "a banana" => 4
);

uksort($a, "cmp");
foreach ($a as $key => $value) {
    echo "$key: $value\n";
}
?>

Output:

an apple: 3
a banana: 4
the Earth: 2
John: 1

The output shows the array reordered by ignoring leading articles ("a", "an", "the") in the keys.