如何在迭代时删除SimpleXMLElement？ （PHP）

I load and run a cycle through my XML structure:

$xml = simplexml_load_file(flakk);
foreach ($xml->class as $class)
{
    now how to delete $class ???
}

the unset($class) has no effect.

You cant remove foreach element, but can for example so

for($i=count($xml->class); $i--; ) unset($xml->class[$i]);

Or

for($i=count($xml->class); $i--; )  
   if ($xml->class[$i] == AnyValue)   
       unset($xml->class[$i]);