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.
Unlike array_diff_key a user supplied callback function is used for the indices comparison, not internal function.
The array to compare from
Arrays to compare against
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.callback(mixed$a,mixed$b ): int
Returns an array containing all the entries from array that are not present in any of the other arrays.
This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff_ukey($array1, $array2, 'callback_func');.