The "array_udiff()" function computes the difference of arrays by using a callback function for data comparison.

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

In the above syntax "array2" is compared with "array1" in a user defined function,to return the elements of "array1" in an array.

    <?php
    function funct1($x1,$x2) 
     {
      if ($x1===$x2)
	 {
	  return 0;
	 }
      return 1;
     }
    $a1=array("a"=>"Orange","b"=>"Guava","c"=>"Apple");
    $b2=array("1"=>"Orange","2"=>"Guava","3"=>"Cherry");
    print_r(array_udiff($a1,$b2,"funct1"));
    ?>

  Array ([c]=> Apple)

In the above example the arrays are compared for difference using "funct1", then the difference values are returned in an array.