array_diff_key(): Difference between two arrays with respect to Keys

$new_array = array_diff_key ($array1, $array2,....);

Comparison of two or more arrays are done by using values in array_diff()

Example with two arrays

$first=array('One' =>'First','Two'=>'Second','Three'=>'Third','Four'=>'Fourth');
$second=array('One'=> 'First','Two'=>'2nd','Third'=>'3rd','Fourth'=>'Fourth');

$result1=array_diff_key($first,$second);
while (list ($key, $val) = each ($result1)) {
echo "$key -> $val <br>";
}

Three -> Third 
Four -> Fourth