array_diff_key Computes the difference of arrays using keys for comparison &reftitle.description; arrayarray_diff_key arrayarray arrayarrays 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. &reftitle.parameters; array The array to compare from arrays Arrays to compare against &reftitle.returnvalues; Returns an array containing all the entries from array whose keys are absent from all of the other arrays. &reftitle.examples; The two keys from the key => value pairs are considered equal only if (string) $key1 === (string) $key2 . In other words a strict type check is executed so the string representation must be the same. 1, 'red' => 2, 'green' => 3, 'purple' => 4); $array2 = array('green' => 5, 'yellow' => 7, 'cyan' => 8); var_dump(array_diff_key($array1, $array2)); ?> ]]> &example.outputs; int(1) ["red"]=> int(2) ["purple"]=> int(4) } ]]> 1, 'red' => 2, 'green' => 3, 'purple' => 4); $array2 = array('green' => 5, 'yellow' => 7, 'cyan' => 8); $array3 = array('blue' => 6, 'yellow' => 7, 'mauve' => 8); var_dump(array_diff_key($array1, $array2, $array3)); ?> ]]> &example.outputs; int(2) ["purple"]=> int(4) } ]]> &reftitle.notes; This function only checks one dimension of a n-dimensional array. Of course you can check deeper dimensions by using array_diff_key($array1[0], $array2[0]);. &reftitle.seealso; array_diff array_udiff array_diff_assoc array_diff_uassoc array_udiff_assoc array_udiff_uassoc array_diff_ukey array_intersect array_intersect_assoc array_intersect_uassoc array_intersect_key array_intersect_ukey