php - 按父/子 ID 重组数组。递归？

Question

我有一组位置。这些位置中的每一个都可以有子位置。每个子位置也可以有子位置，依此类推:

$locations = array(
    array("id" => 1,  "parent_id" => 0, "name" => "England"),
    array("id" => 2,  "parent_id" => 0, "name" => "Scotland"),
    array("id" => 3,  "parent_id" => 0, "name" => "Ireland"),
    array("id" => 4,  "parent_id" => 0, "name" => "Wales"),
    array("id" => 5,  "parent_id" => 1, "name" => "East England"),
    array("id" => 6,  "parent_id" => 1, "name" => "London"),
    array("id" => 7,  "parent_id" => 6, "name" => "West London"),
    array("id" => 8,  "parent_id" => 6, "name" => "East London"),
    array("id" => 9,  "parent_id" => 1, "name" => "East Midlands"),
    array("id" => 10, "parent_id" => 9, "name" => "Derbyshire")
);

我想重新构建这个数组，使子数组成为父数组。像这样的东西(未经测试):

$locations =    array("id" => 1, "parent_id" => 0, "name" => "England", "children" => array(
                    array("id" => 5,  "parent_id" => 1, "name" => "East England"),
                    array("id" => 6,  "parent_id" => 1, "name" => "London", "children" => array(
                            array("id" => 7,  "parent_id" => 6, "name" => "West London"),
                            array("id" => 8,  "parent_id" => 6, "name" => "East London")))));

这样我就可以像这样使用缩进打印出来:

LOCATIONS

England
- East England
- London
-- West London
-- East London
- East Midlands
-- Derbyshire
Scotland
Ireland
Wales

我已经尝试了几种方法，比如按父 ID 对它们进行分组，但我就是无法理解其中的逻辑，可能有更好的方法(递归，也许？)。

非常感谢。

Answer 1

您好，也许这会对您有所帮助，我只是编写它来快速将包含 parent_id 的 mysql 结果转换为可用的数据层次结构。您的输入数组也应该有效。它只是带有两个基本循环的几行代码。不需要递归。一些评论包括:

<?php

$max = count($inputArray);
$tree = array();
$flat = array();
// Create a flat hierarchy array of all entries by their id
for ($i = 0; $i < $max; $i++) {
        $n = $inputArray[$i];
        $id = $n['page_id'];
        $flat[$id] = $n;
}
// Then check all those entries by reference
foreach ($flat as $key => &$child) {
        // Add a children array if not already existing
        if (!isset($child['children']))
                $child['children'] = array();

        $id = $child['page_id'];
        $pid = $child['parent_id'];

        // If childs parent id is larger then zero
        if ($pid > 0) {
                // Append it by reference, which means it will reference
                // the same object across different carriers
                $flat[$pid]['children'][] = &$child;
        } else {
                // Otherwise it is zero level, which initiates the tree
                $tree[$id] = &$child;
        }
}

$tree = array_values($tree); // Indices fixed, there we go, use $tree further
?>

所以请注意“& 引用”字符。它们完成所有工作，允许通过指向相同的对象从平面数组构建树。