php options递归树形数组以及一维数组转换

php代码如下：
public function index(){
        $data = array(
            array('id'=>'1','title'=>'一级栏目','pid'=>0),
            array('id'=>'2','title'=>'二级栏目','pid'=>1),
            array('id'=>'3','title'=>'三级栏目','pid'=>2),
            array('id'=>'4','title'=>'四级栏目','pid'=>3),
            array('id'=>'5','title'=>'一级菜单','pid'=>0),
            array('id'=>'6','title'=>'二级菜单','pid'=>5),
            array('id'=>'7','title'=>'三级菜单','pid'=>6),
            array('id'=>'8','title'=>'四级菜单','pid'=>7),
            array('id'=>'9','title'=>'一级导航','pid'=>0),
            array('id'=>'10','title'=>'二级导航','pid'=>9),
            array('id'=>'11','title'=>'三级导航','pid'=>10),
            array('id'=>'12','title'=>'四级导航','pid'=>11),
        );
        
        //$treeData = $this->treeData($data);
        //print_r($treeData);
        
        $treeData = $this->optionsData($data);
        print_r($treeData);
    }
    //树形数组
    protected function treeData($data,$pid = 0){
        $result = array();
        foreach($data as $v){
            if($v['pid'] == $pid){
                $v['children'] = $this->treeData($data,$v['id']);
                $result[] = $v;
            }
        }
        return $result;
    }
    
    //options递归信息
    protected function optionsData($data,$pid = 0,$level=0,$delimit = ''){
        $result = '';
        foreach($data as $v){
            if($v['pid'] == $pid){
                if($level){
                    for($i=1;$i<=$level;$i++){
                        $delimit .= '&nbsp;&nbsp;';
                    }
                } else {
                    $delimit = '';
                }
                $result .= '<option value="'.$v['id'].'">'.$delimit.$v['title'].'</option>';
                $result .= $this->optionsData($data,$v['id'],$level+1);
            }
        }
        return $result;
    }
    //树形多维数组转换成一维数组
    protected function treeOneData($data,$pid = 0,$level=0,$delimit = ''){
        $result = array();
        foreach($data as $v){
            if($v['pid'] == $pid){
                if($level){
                    for($i=1;$i<=$level;$i++){
                        $delimit .= '&nbsp;&nbsp;';
                    }
                } else {
                    $delimit = '';
                }
                $result[] = '<option value="'.$v['id'].'">'.$delimit.$v['title'].'</option>';
                $res = $this->optionsData($data,$v['id'],$level+1);
                if(is_array($res)){
                    foreach($res as $v2){
                        $result[] = $v2;
                    }
                }
            }
        }
        return $result;
    }