PHP unlimited classification tree data formatting code

function genTree($items,$id='id',$pid='pid',$son = 'children'){
  $tree = array(); //格式化的树
  $tmpMap = array(); //临时扁平数据
    
  foreach ($items as $item) {
    $tmpMap[$item[$id]] = $item;
  }
    
  foreach ($items as $item) {
    if (isset($tmpMap[$item[$pid]])) {
      $tmpMap[$item[$pid]][$son][] = &$tmpMap[$item[$id]];
    } else {
      $tree[] = &$tmpMap[$item[$id]];
    }
  }
  unset($tmpMap);
  return $tree;
}
  
$items1 = array(
    array('id' => 1, 'pid' => 0, 'name' => '一级11' ),
    array('id' => 11, 'pid' => 0, 'name' => '一级12' ),
    array('id' => 2, 'pid' => 1, 'name' => '二级21' ),
    array('id' => 10, 'pid' => 11, 'name' => '二级22' ),
    array('id' => 3, 'pid' => 1, 'name' => '二级23' ),
    array('id' => 12, 'pid' => 11, 'name' => '二级24' ),
    array('id' => 9, 'pid' => 1, 'name' => '二级25' ),
    array('id' => 14, 'pid' => 1, 'name' => '二级26' ),
    array('id' => 4, 'pid' => 9, 'name' => '三级31' ),
    array('id' => 6, 'pid' => 9, 'name' => '三级32' ),
    array('id' => 7, 'pid' => 4, 'name' => '四级41' ),
    array('id' => 8, 'pid' => 4, 'name' => '四级42' ),
    array('id' => 5, 'pid' => 4, 'name' => '四级43' ),
    array('id' => 13, 'pid' => 4, 'name' => '四级44' ),
    array('id' => 15, 'pid' => 8, 'name' => '五级51' ),
    array('id' => 16, 'pid' => 8, 'name' => '五级52' ),
    array('id' => 17, 'pid' => 8, 'name' => '五级53' ),
    array('id' => 18, 'pid' => 16, 'name' => '六级64' ),
); 
var_dump(genTree($items1));

/**
 * 此方法由@Tonton 提供
 * http://my.oschina.net/u/918697
 * @date 2012-12-12
 */
function genTree5($items) {
  foreach ($items as $item)
    $items[$item['pid']]['son'][$item['id']] = &$items[$item['id']];
  return isset($items[0]['son']) ? $items[0]['son'] : array();
}

/**
 * 将数据格式化成树形结构
 * @author Xuefen.Tong
 * @param array $items
 * @return array
 */
function genTree9($items) {
  $tree = array(); //格式化好的树
  foreach ($items as $item)
    if (isset($items[$item['pid']]))
      $items[$item['pid']]['son'][] = &$items[$item['id']];
    else
      $tree[] = &$items[$item['id']];
  return $tree;
}
  
$items = array(
  1 => array('id' => 1, 'pid' => 0, 'name' => '江西省'),
  2 => array('id' => 2, 'pid' => 0, 'name' => '黑龙江省'),
  3 => array('id' => 3, 'pid' => 1, 'name' => '南昌市'),
  4 => array('id' => 4, 'pid' => 2, 'name' => '哈尔滨市'),
  5 => array('id' => 5, 'pid' => 2, 'name' => '鸡西市'),
  6 => array('id' => 6, 'pid' => 4, 'name' => '香坊区'),
  7 => array('id' => 7, 'pid' => 4, 'name' => '南岗区'),
  8 => array('id' => 8, 'pid' => 6, 'name' => '和兴路'),
  9 => array('id' => 9, 'pid' => 7, 'name' => '西大直街'),
  10 => array('id' => 10, 'pid' => 8, 'name' => '东北林业大学'),
  11 => array('id' => 11, 'pid' => 9, 'name' => '哈尔滨工业大学'),
  12 => array('id' => 12, 'pid' => 8, 'name' => '哈尔滨师范大学'),
  13 => array('id' => 13, 'pid' => 1, 'name' => '赣州市'),
  14 => array('id' => 14, 'pid' => 13, 'name' => '赣县'),
  15 => array('id' => 15, 'pid' => 13, 'name' => '于都县'),
  16 => array('id' => 16, 'pid' => 14, 'name' => '茅店镇'),
  17 => array('id' => 17, 'pid' => 14, 'name' => '大田乡'),
  18 => array('id' => 18, 'pid' => 16, 'name' => '义源村'),
  19 => array('id' => 19, 'pid' => 16, 'name' => '上坝村'),
);
 
print_r(genTree5($items));
print_r(genTree9($items));
//后者输出格式，前者类似，只是数组键值不一样，不过不影响数据结构
 
/*
Array
(
[0] => Array
  (
    [id] => 1
    [pid] => 0
    [name] => 江西省
    [son] => Array
      (
        [0] => Array
          (
            [id] => 3
            [pid] => 1
            [name] => 南昌市
          )
  
        [1] => Array
          (
            [id] => 13
            [pid] => 1
            [name] => 赣州市
            [son] => Array
              (
                [0] => Array
                  (
                    [id] => 14
                    [pid] => 13
                    [name] => 赣县
                    [son] => Array
                      (
                      [0] => Array
                        (
                          [id] => 16
                          [pid] => 14
                          [name] => 茅店镇
                          [son] => Array
                            (
                            [0] => Array
                              (
                              [id] => 18
                              [pid] => 16
                              [name] => 义源村
                              )
  
                            [1] => Array
                              (
                              [id] => 19
                              [pid] => 16
                              [name] => 上坝村
                              )
  
                            )
  
                        )
  
                      [1] => Array
                        (
                          [id] => 17
                          [pid] => 14
                          [name] => 大田乡
                        )
  
                      )
  
                  )
  
                [1] => Array
                  (
                    [id] => 15
                    [pid] => 13
                    [name] => 于都县
                  )
  
              )
  
          )
  
      )
  
  )
  
[1] => Array
  (
    [id] => 2
    [pid] => 0
    [name] => 黑龙江省
    [son] => Array
      (
        [0] => Array
          (
            [id] => 4
            [pid] => 2
            [name] => 哈尔滨市
            [son] => Array
              (
              [0] => Array
                (
                  [id] => 6
                  [pid] => 4
                  [name] => 香坊区
                  [son] => Array
                    (
                    [0] => Array
                      (
                        [id] => 8
                        [pid] => 6
                        [name] => 和兴路
                        [son] => Array
                          (
                            [0] => Array
                              (
                              [id] => 10
                              [pid] => 8
                              [name] =>
                               东北林业大学
                              )
  
                            [1] => Array
                              (
                              [id] => 12
                              [pid] => 8
                              [name] =>
                              哈尔滨师范大学
                              )
  
                          )
  
                      )
  
                    )
  
                )
  
              [1] => Array
                (
                  [id] => 7
                  [pid] => 4
                  [name] => 南岗区
                  [son] => Array
                    (
                    [0] => Array
                      (
                      [id] => 9
                      [pid] => 7
                      [name] => 西大直街
                      [son] => Array
                        (
                        [0] => Array
                          (
                          [id] => 11
                          [pid] => 9
                          [name] =>
                           哈尔滨工业大学
                          )
  
                        )
  
                      )
  
                    )
  
                )
  
              )
  
          )
  
        [1] => Array
          (
            [id] => 5
            [pid] => 2
            [name] => 鸡西市
          )
  
      )
  
  )
)*/