The "array_diff" function computes the difference of arrays.

    array_diff (array1,array2,array3.....)

In the above syntax "array1" is the array to be compare with the values of "array2", and display the difference as the result.

    <?php
    $a = array("a" => "green", "red", "blue", "red");
    $b = array("b" => "green", "yellow", "red");
    $result = array_diff($a,$b);
    print_r($result);
    ?>

    Array
     (
      [1] => blue
     )

In the above example array "$a" is compared with array "$b" , the only elements that is not present in the array "$b" is "blue".