How to get hierarchy path of an element in an Array

[awawayBluenue]

I always want to get the exact path of an element in an array. Example array:array(a=>'aaa', 'b'=> array ('bbb1', 'bbb2' => array('bbb3', 'bbb4')));So, for reaching to 'bbb4', I need to go through (b => bbb2 => bbb4). How to get this path in multidimensional array?