PHPで無限分類を実装する方法

$area = array(
array('id'=>1,'name'=>'安徽','parent'=>0),
array('id'=>2,'name'=>'海淀','parent'=>7),
array('id'=>3,'name'=>'濉溪县','parent'=>5),
array('id'=>4,'name'=>'昌平','parent'=>7),
array('id'=>5,'name'=>'淮北','parent'=>1),
array('id'=>6,'name'=>'朝阳','parent'=>7),
array('id'=>7,'name'=>'北京','parent'=>0),
array('id'=>8,'name'=>'上地','parent'=>2)
);

function subtree($arr,$id=0,$lev=1) {
    $subs = array(); // 子孙数组
    foreach($arr as $v) {
        if($v['parent'] == $id) {
            $v['lev'] = $lev;
            $subs[] = $v; // 举例说找到array('id'=>1,'name'=>'安徽','parent'=>0),
            $subs = array_merge($subs,subtree($arr,$v['id'],$lev+1));
        }
    }
    return $subs;
}
$tree = subtree($area,0,1);
foreach($tree as $v) {
    echo str_repeat(&#39;  &#39;,$v[&#39;lev&#39;]),$v[&#39;name&#39;],&#39;<br />&#39;;
}

function familytree($arr,$id) {
    $tree = array();
    foreach($arr as $v) {
        if($v['id'] == $id) {// 判断要不要找父栏目
            if($v['parent'] > 0) { // parnet>0,说明有父栏目
                $tree = array_merge($tree,familytree($arr,$v['parent']));
            }
            $tree[] = $v; // 以找到上地为例
        }
    }
    return $tree;
}
print_r(familytree($area,8)); // 北京->海淀->上地

// 迭代,效率比递归高,代码也没多.
// 找家谱树推荐用迭代
function tree($arr,$id) {
    $tree = array();
    while($id !== 0) {
        foreach($arr as $v) {
            if($v['id'] == $id) {
                $tree[] = $v;
                $id = $v['parent'];
                break;
            }    
        }
    }
    return $tree;
}
print_r(tree($area,8));