php多级归类查询

php多级分类查询
http://www.oschina.net/question/167679_56466 类似这种效果，要怎么实现，还是有更好的方法

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PHP code

$a = Array(  '0' => Array('id' => 3,'sid' => 0),  '1' => Array('id' => 4,'sid' => 0),  '2' => Array('id' => 5,'sid' => 3),  '3' => Array('id' => 6,'sid' => 0),  '4' => Array('id' => 7,'sid' => 4),  '5' => Array('id' => 8,'sid' => 0),);function cmsort($ar, $sid=0, &$res=array()) {  foreach($ar as $r) {    if($r['sid'] == $sid) {      $res[] = $r;      cmsort($ar, $r['id'], $res);    }  }  return $res;}var_export(cmsort($a));<div class="clear"></div>