array_diff_key

Syntax:array array_diff_key ( array $array1 , array $array2 [, array $... ] ) Description:Computes the difference of arrays using keys for comparison
<?php
$array1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);

print_r(array_diff_key($array1, $array2));
?>
OUTPUT
Array ( 
[red] => 2 
[purple] => 4 
)