PHP array_diff_key() function
This is an inbuilt function of PHP. This function was introduced in PHP 5.1. The array_diff_key() function compares the keys of two or more arrays, and returns entries from array1 that are not present in array2 or array3, etc.
Returns an array containing the entries from array1 that are not present in any of the other arrays.
Array ( => Boi )
Array(  => Laxman  => Rahul  => Ganguly  => Yuvi )
Array ( [b] => Bed )
Array ( [a1]=> red [c3]=> blue [d4]=> black )