array_diff_ukey()

array_diff_ukey() — Computes the difference of arrays using a callback function on the keys for comparison.

Built-in function of PHP 8.5. The manual lists it as available in PHP 5 >= 5.1.0, PHP 7, PHP 8. This page is the reference card: signature, parameters and return value, plus the changelog and the example the manual provides.

What it does

Compares the keys from array against the keys from arrays and returns the difference. This function is like array_diff() except the comparison is done on the keys instead of the values.

Signature

array_diff_ukey(array $array, array ...$arrays, callable $key_compare_func): array callback(mixed $a, mixed $b): int

Parameters

Parameter	Type	What it takes
$array	array	The array to compare from
...$arrays	array	Arrays to compare against
$key_compare_func	callable	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.

Return value

Returns an array containing all the entries from array that are not present in any of the other arrays.

Example

A runnable snippet:

function key_compare_func($key1, $key2) { if ($key1 == $key2) return 0; else if ($key1 > $key2) return 1; else return -1; } $array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4); $array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8); var_dump(array_diff_ukey($array1, $array2, 'key_compare_func'));

Output:

array(2) { ["red"]=> int(2) ["purple"]=> int(4) }