array_udiff_assoc() – Compute Array Difference with Index Check Using Callback Comparison

The array_udiff_assoc() function in PHP calculates the difference between two arrays while also comparing their keys, using a user‑provided callback function to determine how values are compared.

Parameters: array $array1 – the first array; array $array2 – the second array; callable $data_compare_func – a callback that must return an integer less than, equal to, or greater than zero when the first argument is considered less than, equal to, or greater than the second.

Return value: An array containing all values from $array1 that are not present in any of the other arrays, with key comparison performed using the supplied callback.

Example:

<?php
class cr {
    private $priv_member;
    function __construct($val) {
        $this->priv_member = $val;
    }
    public static function comp_func_cr($a, $b) {
        if ($a->priv_member === $b->priv_member) return 0;
        return ($a->priv_member > $b->priv_member) ? 1 : -1;
    }
}

$a = array(
    "0.1" => new cr(9),
    "0.5" => new cr(12),
    0 => new cr(23),
    1 => new cr(4),
    2 => new cr(-15)
);

$b = array(
    "0.2" => new cr(9),
    0 => new cr(22),
    1 => new cr(3),
    2 => new cr(4)
);

$result = array_udiff_assoc($a, $b, array('cr', 'comp_func_cr'));
print_r($result);
?>

Output:

Array
(
    [0.1] => cr Object
        (
            [priv_member] => 9
        )
    [0.5] => cr Object
        (
            [priv_member] => 12
        )
    [0] => cr Object
        (
            [priv_member] => 23
        )
    [1] => cr Object
        (
            [priv_member] => 4
        )
    [2] => cr Object
        (
            [priv_member] => -15
        )
)