Is there a good way to iterate over the numeric keys only in an array with mixed numeric and associative keys, other than brute force where you use do a foreach() and then use something like is_numeric() the individual keys?

For instance I have an array like
PHP Code:
$array = array('0'=>'zero''1'=>'one''2'=>'two''3'='three''fruit'=>'orange''color'=>'green''plant'=>'grass'); 
And I want to iterate over the 0, 1, 2, and 3 elements only.