这样的xml怎么循环

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);