PHP 将无限极分类数组 转换为纵向表格

class Index extends Common
{
   

   public function test()
   {
      $data_list = [
         [
            'id'   => 1,
            'pid'  => 0,
            'name' => 'A1'
         ], [
            'id'   => 2,
            'pid'  => 0,
            'name' => 'A2'
         ], [
            'id'   => 3,
            'pid'  => 0,
            'name' => 'A3'
         ], [
            'id'   => 4,
            'pid'  => 3,
            'name' => 'A4'
         ], [
            'id'   => 5,
            'pid'  => 2,
            'name' => 'A5'
         ], [
            'id'   => 6,
            'pid'  => 2,
            'name' => 'A6'
         ], [
            'id'   => 7,
            'pid'  => 0,
            'name' => 'A7'
         ], [
            'id'   => 8,
            'pid'  => 3,
            'name' => 'A8'
         ], [
            'id'   => 9,
            'pid'  => 3,
            'name' => 'A9'
         ],
      ];

      $vertical = $this->data_conversion($data_list);

      $this->table($vertical);


   }

   /**
    * 数据转换   简陋算法   有空再优化
    * @param $data_list
    * @return array
    */
   public function data_conversion($data_list)
   {
      $parents = [];
      foreach ($data_list as $key => $item) {
         if ($item['pid'] === 0) {
            $data = Tree::getChilds($data_list, $item['id']);
            array_unshift($data, $item);
            $parents[] = $data;
         }
      }

      $vertical = [];
      $num = [];
      foreach ($parents as $key => $parent) {
         $num[$key] = count($parent);
      }
      foreach ($parents as $key => $parent) {
         $x = max($num) - count($parent);
         foreach ($parent as $k => $item) {
            $vertical[$k][$key] = $item;
         }

         for ($i = count($parent); $i <= count($parent) + $x - 1; $i ++) {
            $vertical[$i][$key] = ['name' => ''];
         }
      }
      return $vertical;
   }

   /**
    * 遍历表格
    * @param $vertical
    */
   public function table($vertical)
   {

      $table = '<br><table border="1" cellspacing="0" cellpadding="0">';
      foreach ($vertical as $parent) {
         $table .= '<tr>';
         foreach ($parent as $item) {
            $table .= '<td>' . $item['name'] . '</td>';
         }
         $table .= '</tr>';
      }
      $table .= '</table><br>';
      echo $table;
   }

   /**
    * 获取所有子节点
    * @param  array $lists 数据集
    * @param  string $pid 父级id
    * @return array
    */
   public static function getChilds($lists = [], $pid = '')
   {
      $result = [];
      foreach ($lists as $value) {
         if ($value[self::$config['pid']] == $pid) {
            $result[] = $value;
            $result = array_merge($result, self::getChilds($lists, $value[self::$config['id']]));
         }
      }
      return $result;
   }

}