前段时间做一个小项目的时候用到了无限级分类，当时也忘的差不多了，于是就去网上查资料学，下面是我的学习笔记

数据格式:

array (size=5)

  1 =>

    array (size=6)

      'id' => string '1' (length=1)

      'pid' => string '0' (length=1)

      'name' => string '青年之声1' (length=13)

      'description' => string '' (length=0)

      'create_time' => string '2017-04-02 15:38:06' (length=19)

      'del' => string '0' (length=1)

  2 =>

    array (size=6)

      'id' => string '2' (length=1)

      'pid' => string '1' (length=1)

      'name' => string '青年之声2' (length=13)

      'description' => string '' (length=0)

      'create_time' => string '2017-04-02 15:38:06' (length=19)

      'del' => string '0' (length=1)

  3 =>

    array (size=6)

      'id' => string '3' (length=1)

      'pid' => string '2' (length=1)

      'name' => string '青年之声3' (length=13)

      'description' => string '' (length=0)

      'create_time' => string '2017-04-02 15:38:06' (length=19)

      'del' => string '0' (length=1)

  4 =>

    array (size=6)

      'id' => string '4' (length=1)

      'pid' => string '3' (length=1)

      'name' => string '青年之声4' (length=13)

      'description' => string '' (length=0)

      'create_time' => string '2017-04-02 15:38:06' (length=19)

      'del' => string '0' (length=1)

  5 =>

    array (size=6)

      'id' => string '5' (length=1)

      'pid' => string '4' (length=1)

      'name' => string '青年之声5' (length=13)

      'description' => string '' (length=0)

      'create_time' => string '2017-04-02 15:38:06' (length=19)

      'del' => string '0' (length=1)

非递归算法

$tree = array();

foreach ($items as $item) {

	if (isset($items[$item['pid']])) {

		$items[$item['pid']]['childs'][] = &$items[$item['id']];

	} else {

		$tree[] = &$items[$item['id']];

	}

}

递归算法

function getChild($id) {

	$tree = [];

	$childs = Columns::find()->where(['pid' => $id, 'del' => 0])->asArray()->all();

	if ($childs) {

		foreach ($childs as $child) {

			$childTree = getChild($child['id']);

			if ($childTree) {

				$child['children'] = $childTree;

			}

			$tree[] = $child;

		}

	}

	return $tree;

}

最终结果