无限级分类三种方法

  function sort($category,$parent_id=0,$level=0){
        static $arr=array();
        foreach($category as $k=>$v){
            if($v['parent_id']==$parent_id){
                $v['level']=$level;
                $arr[]=$v;
                unset($category[$k]);//已经排好等级的,从数组中移除，提高性能
                $this->sort($category,$v['id'],$level+1);
            }
        }
        return $arr;
    }
    
    function sort2($category,$parent_id=0,$level=0){
        $res=array();
        foreach($category as $c){
            if($c['parent_id']==$parent_id){
                $c['level']=$level;
                $arr[]=$c;
                $res=array_merge($arr,$this->sort($category,$c['id'],$level+1));
            }
        }
        return $res;
    }

   /**
    * 得到分类级数，并将他们的上下级关系，体现在返回数组中
    * @param unknown $category
    * @param number $parent_id
    * @param number $level
    * @return multitype:array
    */
   function category($category,$parent_id=0,$level=0){
        $arr=array();
        foreach($category as $k=>$v){
            if($v['parent_id']==$parent_id){
                $v['level']=$level;
                $v['child']=$this->category($category,$v['id'],$level+1);
                $arr[]=$v;
            }
        }
        return $arr;
    }