PHP构建层级（树状）数组

/**
 * 将数组转为tree树形结构函数
 *
 * @param        $list
 * @param string $pk
 * @param string $pid
 * @param string $child
 * @param int    $root
 *
 * @return array
 */
function listToTree($list, $pk = 'id', $pid = 'pid', $child = 'children', $root = 0)
{
    $tree = array();
    if(is_array($list)) {
        // 创建基于主键的数组引用
        $refer = array();
        foreach ($list as $key => $data) {
            $refer[$data[$pk]] =& $list[$key];
        }
        foreach ($list as $key => $data) {
            // 判断是否存在parent
            $parentId = $data[$pid];
            if ($root == $parentId) {
                $tree[] =& $list[$key];
            }else{
                if(isset($refer[$parentId])) {
                    $parent =& $refer[$parentId];
                    $parent[$child][] =& $list[$key];
                }
            }
        }
    }

    return $tree;
}

/**
 * 将数组转为tree树形结构函数
 *
 * @param        $list
 * @param string $pk
 * @param string $pid
 * @param string $child
 * @param int    $root
 *
 * @return array
 */
function listToTree($list, $pk = 'id', $pid = 'pid', $child = 'children', $root = 0)
{
    $tree = array();
    if(is_array($list)) {
        // 创建基于主键的数组引用
        $refer = array();
        foreach ($list as $key => $data) {
            $refer[$data[$pk]] =& $list[$key];
        }
        foreach ($list as $key => $data) {
            // 判断是否存在parent
            $parentId = $data[$pid];
            if ($root == $parentId) {
                $tree[] =& $list[$key];
            }else{
                if(isset($refer[$parentId])) {
                    $parent =& $refer[$parentId];
                    $parent[$child][] =& $list[$key];
                }
            }
        }
    }

    return $tree;
}
/**
 * 数组层级缩进转换
 * @param array $array 源数组
 * @param int   $pid
 * @return array
 */
function array2level($array, $pid = 0, $level = 1)
{
    static $list = [];
    foreach ($array as $v) {
        if ($v['pid'] == $pid) {
            $v['level'] = $level;
            $list[]     = $v;
            self::array2level($array, $v['id'], $level + 1);
        }
    }
    return $list;
}
/**
 * 构建层级（树状）数组
 * @param array  $array          要进行处理的一维数组，经过该函数处理后，该数组自动转为树状数组
 * @param string $pid_name       父级ID的字段名
 * @param string $child_key_name 子元素键名
 * @return array|bool
 */
function array2tree(&$array, $pid_name = 'pid', $child_key_name = 'children')
{
    $counter = self::array_children_count($array, $pid_name);
    if (!isset($counter[0]) || $counter[0] == 0) {
        return $array;
    }
    $tree = [];
    while (isset($counter[0]) && $counter[0] > 0) {
        $temp = array_shift($array);
        if (isset($counter[$temp['id']]) && $counter[$temp['id']] > 0) {
            array_push($array, $temp);
        } else {
            if ($temp[$pid_name] == 0) {
                $tree[] = $temp;
            } else {
                $array =  self::array_child_append($array, $temp[$pid_name], $temp, $child_key_name);
            }
        }
        $counter =  self::array_children_count($array, $pid_name);
    }
    return $tree;
}
/**
 * 把元素插入到对应的父元素$child_key_name字段
 * @param        $parent
 * @param        $pid
 * @param        $child
 * @param string $child_key_name 子元素键名
 * @return mixed
 */
function array_child_append($parent, $pid, $child, $child_key_name)
{
    foreach ($parent as &$item) {
        if ($item['id'] == $pid) {
            if (!isset($item[$child_key_name])) {
                $item[$child_key_name] = [];
            }
            
            $item[$child_key_name][] = $child;
        }
    }
    return $parent;
}
/**
 * 子元素计数器
 * @param array $array
 * @param int   $pid
 * @return array
 */
function array_children_count($array, $pid)
{
    $counter = [];
    foreach ($array as $item) {
        $count = isset($counter[$item[$pid]]) ? $counter[$item[$pid]] : 0;
        $count++;
        $counter[$item[$pid]] = $count;
    }
    return $counter;
}