The "array_intersect_ukey()" function is used to compute the intersection of array elements using a callback function on the keys for comparison.

    array_intersect_ukey(array1,array2,array3....,function)

In the above syntax values and keys of "array1" is compared with other arrays using keys and again checked in the function for keys. The values and keys are returned in a array

The difference between array_intersect_ukey() and array_intersect_key() is that array_intersect_ukey() function uses a user defined function to find the intersecting array elements using keys.

    <?php
    function func1($k1, $k2)
     {
      if ($k1 == $k2)
        return 0;
      else if ($k1 > $k2)
        return 1;
      else
        return -1;
      }
    $a = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
    $b = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);
    var_dump(array_intersect_ukey($a, $b, 'func1'));
    ?>

    array(2) {["blue"]=> int(1) ["green"]=> int(3)}

In the above example the two arrays "$a","$b" are compared for array elements keys automatically, then compared for keys in the function. It returns intersection result of both the values and keys.