Using array_udiff() with a Callback Function to Compute Array Differences in PHP

array_udiff() returns an array containing all values from array1 that are not present in any of the other arrays, while preserving the original keys. The comparison of values is performed by a user‑defined callback function supplied as data_compare_func.

Parameters :

array1 – the first array.

array2 – the second array (additional arrays can be passed).

data_compare_func – a callable that receives two values and 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 of the values from array1 that are not found in any of the other arrays, with their original keys preserved.

Example implementation :

<?php
class cr {
    private $priv_member;
    function cr($val) {
        $this->priv_member = $val;
    }
    static function comp_func_cr($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)
);

$b = array(
    "0.2" => new cr(9),
    "0.5" => new cr(12),
    0      => new cr(3),
    1      => new cr(4),
    2      => new cr(-15)
);

$result = array_udiff($a, $b, "cr::comp_func_cr");
print_r($result);
?>

The script prints the resulting array, showing the elements that are unique to $a according to the custom comparison logic. In this case the output is:

Array
(
    [0.5] => cr Object
        (priv_member => 12)
    [0] => cr Object
        (priv_member => 23)
)