array_intersect_ukey ( array1,array2 [, array3..., callbackkey_compare_func] );

<?php
   function key_compare_func(k1,k2) {
      if (k1 ==k2)
         return 0;

      else if (k1>k2)
         return 1;

      else
         return -1;
   }

   input1 = array('blue'=>1, 'red'=>2, 'green'=>3, 'purple'=>4);input2 = array('green'=>5, 'blue'=>6, 'pink'=>7, 'black'=>8);

   result = array_intersect_ukey(input1, input2, "key_compare_func");
   var_dump(result);
?>

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