Assign values in foreach-loop

Hello to all, is it possible to assign values to the array for which I do the foreach-loop? foreach ($_SESSION['arr1'] as $arr1) { foreach ($_SESSION['arr2'] as $arr2) {

       if ($arr1['id'] == $arr2['id']) {
           $arr1['selected'] = true;
       }
   }   }

I think $arr1 is only a temp-var, so the assignment won't reflect on $_SESSION['arr1'] . Is that right? Surely I can do it with a for-loop, but those arrays are a bit complex and a foreach would be much easier to read. Thanks in advance for your answers Sabine