PHP. How to form a dynamic multidimensional array?

Question

PHP

The database has a category table. Categories have a hierarchical structure. Displaying them in the form of a tree with echo-m li-shkas is easy (I do it using recursion). But here's how to form a multidimensional array?
UPD
Example.
There is a large diameter pipeline:
id | parent_id
2 | 1
3 | 1
4 | 2
5 | 2
The output should be such an array (I convey the meaning itself, you can of course arrange it differently, for example, use the 'childs' subarrays, and also take into account the root category in the real code):

$array = [
  0=>[
    'node'=>1,
    0=>['node'=>2, 0=>4, 1=>5],
    1=>3,
  ],	
];

//those. each node that has a subcategory is an Array. A node with no categories is just a value. In this case, the 2nd categories contain child elements/subcategories, so there are only 2 arrays.

Answer 1

Without using links, the tree is built like this:

<?php

error_reporting(E_ALL);
ini_set('display_errors', 1);
ini_set('xdebug.var_display_max_depth', -1);

$items = [
    ['id' => 1, 'name' => 'A',          'parent' => 0],
    ['id' => 2, 'name' => 'A-1',        'parent' => 1],
    ['id' => 3, 'name' => 'A-1-1',      'parent' => 2],
    ['id' => 5, 'name' => 'A-1-1-2',    'parent' => 3],
    ['id' => 6, 'name' => 'A-2',        'parent' => 1],
    ['id' => 7, 'name' => 'A-2-2-1',    'parent' => 6],
    ['id' => 4, 'name' => 'A-1-1-1',    'parent' => 3],
    ['id' => 8, 'name' => 'A-2-2-2',    'parent' => 6],
    ['id' => 9, 'name' => 'A-2-2-1-1',  'parent' => 7],
    ['id' => 10,'name' => 'B',          'parent' => 0],
];

function buildTree(array $items, $parent = 0)
{
    $tree = array();
    foreach ($items as $item) {
        if ($item['parent'] === $parent) {
            $children = buildTree($items, $item['id']);
            if ($children) {
                $item['children'] = $children;
            }
            $tree[] = $item;
        }
    }

    return $tree;
}

function getList($items = [])
{
    $html = '';
    foreach ($items as $item) {
        $html .= vsprintf('<ul><li><span>%s</span>%s</li></ul>', [
            $item['name'],
            empty($item['children']) ? '' : getList($item['children'])
        ]);
    }

    return $html;
}

$tree = buildTree($items);
$list = getList($tree);

echo "<pre>";
echo $list;
var_dump($tree);
echo "</pre>";
exit("File: " . __FILE__ . " Line: " . __LINE__);

Answer 2

More or less like this:

$sql = 'SELECT * FROM `categories`';
$stmt = DBH::PDO()->query($sql)->execute();
$data = [];
while ($row = $stmt->fetch(PDO::FETCH_ASSOC){
  $data[$row['parent']][$row['id']] = $row;
}