The "array_intersect_key()" function is used to compute the intersection of array elements, only if the keys are present in all other arrays.

    array_intersect_key(array1,array2,array3.........)

In the above syntax keys of "array1" is compared with other array elements, to return an array with values of keys that are present in all other arrays.

    <?php
    $a = array (0=>'Blue',1=>'Green', 2=>'Orange', 3=>'Pink');
    $b = array (4=>'Red', 2=>'Green', 3=>'Orange');
    print_r(array_intersect_key($a,$b));
    ?>

    Array ( [2] => Orange [3] => Pink ) 

In the above example the two arrays "$a","$b" when compared for keys, returns "Orange","Pink", as the keys 3,2 are present in both the arrays.