array array_diff_ukey ( array $array1 , array $array2 [, array $ ... ], callback $key_compare_func )
Compares the keys from array1 against the keys from array2 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() an user supplied callback function is used for the indices comparison, not internal function.
Returns an array containing all the entries from array1 that are not present in any of the other arrays.