Checking if array is multidimensional or not?

Question

1. What is the most efficient way to check if an array is a flat array of primitive values or if it is a multidimensional array?

Answer 1

All great answers... here's my three lines that I'm always using

function isMultiArray($a){
    foreach($a as $v) if(is_array($v)) return TRUE;
    return FALSE;
}