array_intersect_ukey Computes the intersection of arrays using a callback function on the keys for comparison arrayarray_intersect_ukey arrayarray1 arrayarray2 array... callbackkey_compare_func array_intersect_ukey returns an array containing all the values of array1 which have matching keys that are present in all the arguments. This comparison is done by a user supplied callback function. It must return an integer less than, equal to, or greater than zero if the first key is considered to be respectively less than, equal to, or greater than the second. $key2) return 1; else return -1; } $array1 = array('blue' => 1, 'red' => 2, 'green' => 3, 'purple' => 4); $array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan' => 8); var_dump(array_intersect_ukey($array1, $array2, 'key_compare_func')); ?> ]]> &example.outputs; int(1) ["green"]=> int(3) }) ]]> In our example you see that only the keys 'blue' and 'green' are present in both arrays and thus returned. Also notice that the values for the keys 'blue' and 'green' differ between the two arrays. A match still occurs because only the keys are checked. The values returned are those of array1. See also array_diff, array_udiff array_diff_assoc, array_diff_uassoc, array_udiff_assoc, array_udiff_uassoc, array_diff_key, array_diff_ukey, array_intersect, array_intersect_assoc, array_intersect_uassoc and array_intersect_key.