$yes = array();
$yes['c'][3] = '';
$yes['a'][0] = '';
$yes['b'][1] = ''; 
$yes['c'][7] = '';
$yes['b'][2] = ''; 
$yes['c'][5] = '';

 array_multisort($yes['a'], SORT_ASC, SORT_NUMERIC
                ,$yes['b'], SORT_NUMERIC, SORT_ASC
                ,$yes['c'], SORT_NUMERIC, SORT_ASC
                );
 asort($yes);
print_r($yes);