Iterate through an array, looking for keys that match the values of another array

This is probably a si开发者_如何学运维mple question...

I have a multidimensional array called $form. I need to iterate through the array, looking for specific keys that match another array values and then perform an action in those keys.

$a = 'theme_select';
$b = 'timezone';
$c = 'contact';
$d = 'something_else';

$arr = array();
$arr = ($a, $b, $c, $d);

foreach($form as $form_key=>$form_val){

    foreach($arr as $include) {

       if ($form_key == $include) {

           //some action

       }
    }
}

Is this the best way to accomplish this? The reason I'm asking is that $form can be quite big and I fear that page loading can become quite slow.

---

Have a look at the array_intersect_key() function

$a = 'theme_select'; 
$b = 'timezone'; 
$c = 'contact'; 
$d = 'something_else';  

$arr = array_fill_keys(array($a, $b, $c, $d),1); 

$matchingKeys = array_intersect_keys($form,$arr);
foreach($matchingKeys as $key => $value) {
   ...
}