/**
 * @Description: 无限极分类一
 * @Author: Yang
 * @param $data  数据库数据
 * @param int $parent_id   父级ID
 * @return array
 */
function getTree1($data, $parent_id = 0) {
	$tree = array();
	foreach ($data as $k => $v) {
		if ($v["parent_id"] == $parent_id) {
			unset($data[$k]);
			if (!empty($data)) {
				$children = getTree1($data, $v["id"]);
				if (!empty($children)) {
					$v["_child"] = $children;
				}
			}
			$tree[] = $v;
		}
	}
	return $tree;
}
/**
 * @Description: 无限极分类二
 * @Author: Yang
 * @param $data   数据库数据
 * @param int $parent_id  父级ID
 * @param int $level  等级
 * @return array
 */
function getTree2($data, $parent_id = 0, $level = 0) {
	static $tree = array();
	foreach ($data as $k => $v) {
		if ($v["parent_id"] == $parent_id) {
			$v["level"] = $level;
			$tree[] = $v;
			getTree2($data, $v["id"], $level + 1);
		}
	}
	return $tree;
}
/**
 * @Description: 无限分类三：面包屑导航
 * @Author: Yang
 * @param $data  数据库数据
 * @param $id    分类ID
 * @return array
 */
function getCrumbsBar($data, $id) {
	static $tree = array();
	foreach ($data as $k => $v) {
		if ($v["id"] == $id) {
			getCrumbsBar($data, $v["parent_id"]);
			$tree[] = $v;
		}
	}
	return $tree;
}

//示例
$arr = array(
    array('id'=>2,'cname'=>'分类2','parent_id'=>1),
    array('id'=>9,'cname'=>'分类9','parent_id'=>8),
    array('id'=>1,'cname'=>'分类1','parent_id'=>0),
    array('id'=>7,'cname'=>'分类7','parent_id'=>0),
    array('id'=>3,'cname'=>'分类3','parent_id'=>2),
    array('id'=>4,'cname'=>'分类4','parent_id'=>0),
    array('id'=>6,'cname'=>'分类6','parent_id'=>5),
    array('id'=>8,'cname'=>'分类8','parent_id'=>7),
    array('id'=>5,'cname'=>'分类5','parent_id'=>4)
);
print_r(getTree1($arr));