如何从 PHP 中的数组构建树结构

Question

我有下表：

$arr = array(
  array('id'=>100, 'year'=>2019, 'month'=>9, 'name'=>'a'),
  array('id'=>101, 'year'=>2019, 'month'=>12, 'name'=>'b'),
  array('id'=>102, 'year'=>2020, 'month'=>1, 'name'=>'c'),
  array('id'=>103, 'year'=>2020, 'month'=>2, 'name'=>'d'),
);

使用下面的代码

$tree = array();
foreach ($arr as $row) {
    $tree[$row['year']] = array(
        $row['month'] => array (
            'id' => $row['id'],
            'name' => $row['name'],
        ),
    );
}

我想得到以下结果 - 这个结构是一棵树：

Array
(
    [2019] => Array
        (
            [9] => Array
                (
                    [id] => 100
                    [name] => a
                )
            [12] => Array
                (
                    [id] => 101
                    [name] => b
                )
        )

    [2020] => Array
        (
            [1] => Array
                (
                    [id] => 102
                    [name] => c
                )
            [2] => Array
                (
                   [id] => 103
                   [name] => d
                )
        )
)

不幸的是，我只得到一个带有单个“分支”的关注：

Array
(
    [2019] => Array
        (
            [12] => Array
                (
                    [id] => 101
                    [name] => b
                )
        )

    [2020] => Array
        (
            [2] => Array
                (
                   [id] => 103
                   [name] => d
                )
        )
)

这里缺少什么？ 为什么前面的行从结构中消失了？

Answer 1

由于您希望年份和月份作为主要索引，因此在将数据添加到$tree时需要同时使用这两个索引...

$tree = array();
foreach ($arr as $row) {
    $tree[$row['year']][$row['month']] = [   'id' => $row['id'],
            'name' => $row['name']];
}

使用您的测试数据，这给出了...

Array
(
    [2019] => Array
        (
            [9] => Array
                (
                    [id] => 100
                    [name] => a
                )

            [12] => Array
                (
                    [id] => 101
                    [name] => b
                )

        )

    [2020] => Array
        (
            [1] => Array
                (
                    [id] => 102
                    [name] => c
                )

            [2] => Array
                (
                    [id] => 103
                    [name] => d
                )

        )

)

Answer 2

您的密钥名称有误 - bl_year, bl_month不存在：

foreach ($arr as $row) {
    $tree[$row['year']] = array(
        $row['month'] => array (
            'id' => $row['id'],
            'name' => $row['name'],
        ),
    );
}