递归无限极分类

<?php
    $area = array(  
    array('id'=>1,'name'=>'安徽','parent'=>0),  
    array('id'=>2,'name'=>'北京','parent'=>0),  
    array('id'=>3,'name'=>'海淀','parent'=>2),  
    array('id'=>4,'name'=>'中关村','parent'=>3),  
    array('id'=>5,'name'=>'合肥','parent'=>1),  
    array('id'=>6,'name'=>'上地','parent'=>3),  
    array('id'=>7,'name'=>'河北','parent'=>0),  
    array('id'=>8,'name'=>'石家庄','parent'=>7),  
    );  

    function cityinfo($arr,$id,$len=1){
        static $sub = array();
        foreach($arr as $v) {
            if($v['parent'] == $id) {
            $v['len'] = $len;
            $sub[] = $v;
            cityinfo($arr,$v['id'],$len+1);
            }
        }
        return $sub;
    }

    $tree = cityinfo($area,0,1);  
  foreach ($tree as $v) {  
   echo str_repeat('&nbsp',$v['len']);
   echo $v['name'];
   echo '<br />';  
}  
?>