How to recursively sort associative array - php

Question

I'd like to sort the following associative array:
$tree = [
"id" => 245974,
"children" => [
[
"id" => 111
],
[
"id" => 245982,
"children" => [
[
"id" => 246093,
"children" => [
[
"id" => 225892
],
[
"id" => 225893
],
[
"id" => 225902
]
]
]
]
]
]
];
Desired sort order after the "search value" of id => 225902:
[
"id" => 245974,
"children" => [
[
"id" => 245982, // <-- this is moved up
"children" => [
[
"id" => 246093,
"children" => [
[
"id" => 225902 // <-- this is moved up
],
[
"id" => 225892
],
[
"id" => 225893
]
]
]
]
],
[
"id" => 111
]
]
];
What I've tried:
<?php
$category_id = 225902;
function custom_sort(&$a, &$b) {
global $category_id;
if ($a['id'] === $category_id) {
return -1;
}
if ($b['id'] === $category_id) {
return 1;
}
if (array_key_exists('children', $a)) {
if (usort($a['children'], "custom_sort")) {
return -1;
}
}
if (array_key_exists('children', $b)) {
if (usort($b['children'], "custom_sort")) {
return 1;
}
}
return 0;
}
function reorder_tree($tree) {
usort($tree['children'], "custom_sort");
return $tree;
}
echo "<pre>";
var_dump(reorder_tree($tree));
echo "</pre>";
However, that returns:
[
"id" => 245974,
"children" => [
[
"id" => 245982, // <- this is moved up
"children" => [
[
"id" => 246093,
"children" => [
[
"id" => 225892
],
[
"id" => 225893
],
[
"id" => 225902 // <- this is *not* moved up
]
]
]
]
],
[
"id" => 111
],
]
];
How would I be able to also sort the children arrays?

Answer 1

Great attempt and very much on the right track. The problem with recursion in the comparator is that usort will not call the comparator function when the array length is 1, so whether or not you explore the whole tree is at the whim of usort. This will abandon id => 245982's branch of the tree.
The solution is to avoid recursing in the usort's comparator function directly. Rather, use a regular recursive function that calls usort as needed, namely, the current array or a child array contains the target id. I use a separate array to keep track of which elements should be moved forward, but you can break out of the loop and splice/unshift a single element to the front if you prefer.
We can also make $category_id a parameter to the function.
Here's one approach:
function reorder_tree_r(&$children, $target) {
$order = [];
$should_sort = false;
foreach ($children as $i => &$child) {
$order[$i] = false;
if (array_key_exists("children", $child) &&
reorder_tree_r($child["children"], $target) ||
$child["id"] === $target) {
$order[$i] = true;
$should_sort = true;
}
}
if ($should_sort) {
$priority = [];
$non_priority = [];
for ($i = 0; $i < count($children); $i++) {
if ($order[$i]) {
$priority[]= $children[$i];
}
else {
$non_priority[]= $children[$i];
}
}
$children = array_merge($priority, $non_priority);
}
return $should_sort;
}
function reorder_tree($tree, $target) {
if (!$tree || !array_key_exists("children", $tree)) {
return $tree;
}
reorder_tree_r($tree["children"], $target);
return $tree;
}
var_export(reorder_tree($tree, 225902));
Output:
array (
'id' => 245974,
'children' =>
array (
0 =>
array (
'id' => 245982,
'children' =>
array (
0 =>
array (
'id' => 246093,
'children' =>
array (
0 =>
array (
'id' => 225902,
),
1 =>
array (
'id' => 225892,
),
2 =>
array (
'id' => 225893,
),
),
),
),
),
1 =>
array (
'id' => 111,
),
),