这样的xml如何循环

SimpleXMLElement Object(    [date] => Array        (            [0] => 周五(今天, 实时：25)            [1] => 周六            [2] => 周日            [3] => 周一        )    [dayPictureUrl] => Array        (            [0] => http://api.map.baidu.com/images/weather/day/qing.png            [1] => http://api.map.baidu.com/images/weather/day/qing.png            [2] => http://api.map.baidu.com/images/weather/day/qing.png            [3] => http://api.map.baidu.com/images/weather/day/duoyun.png        )    [nightPictureUrl] => Array        (            [0] => http://api.map.baidu.com/images/weather/night/qing.png            [1] => http://api.map.baidu.com/images/weather/night/qing.png            [2] => http://api.map.baidu.com/images/weather/night/duoyun.png            [3] => http://api.map.baidu.com/images/weather/night/duoyun.png        )    [weather] => Array        (            [0] => 晴            [1] => 晴            [2] => 晴转多云            [3] => 多云        )    [wind] => Array        (            [0] => 北风3-4级            [1] => 南风微风            [2] => 南风微风            [3] => 南风微风        )    [temperature] => Array        (            [0] => 24 ~ 9            [1] => 21 ~ 10            [2] => 23 ~ 12            [3] => 22 ~ 11        ))

foreach($xml->date as $i=>$v) {  $res[] = array(    'date' => $v,    'dayPictureUrl'=> $xml->dayPictureUrl[$i],    'nightPictureUrl'=> $xml->nightPictureUrl[$i],    'weather' => $xm->weather[$i],  );}print_r($res);