Nesting Array Items Based on a Value - php

Question

I have an array like this:
0 => ['id'=> 1, 'name' => 'A', 'parent_id' => null],
1 => ['id'=> 2, 'name' => 'A', 'parent_id' => 1],
2 => ['id'=> 3, 'name' => 'A', 'parent_id' => 2],
3 => ['id'=> 4, 'name' => 'A', 'parent_id' => 2],
4 => ['id'=> 5, 'name' => 'A', 'parent_id' => 4]
How can I iterate over this to create a nested array where items are inside of each other based on their parent_id?
Result to look like something like this:
0 => ['id'=> 1, 'name' => 'A', 'parent_id' => null, 'children' => [['id'=> 2, 'name' => 'A', 'parent_id' => 1, 'children' => [['id'=> 3, 'name' => 'A', 'parent_id' => 2], ['id'=> 4, 'name' => 'A', 'parent_id' => 2, 'children' => [['id'=> 4, 'name' => 'A', 'parent_id' => 4]]]]]]]

Answer 1

Use recursive function :
$arr = array(
0 => ['id'=> 1, 'name' => 'A', 'parent_id' => null],
1 => ['id'=> 2, 'name' => 'A', 'parent_id' => 1],
2 => ['id'=> 3, 'name' => 'A', 'parent_id' => 1],
3 => ['id'=> 4, 'name' => 'A', 'parent_id' => 2],
);
function add_childs(array $elements, $parentId = null) {
$parent = array();
foreach ($elements as $element) {
if ($element['parent_id'] == $parentId) {
echo "in if".$element['id']."<br>";
$children = add_childs($elements, $element['id']);
if ($children) {
$element['children'] = $children;
}
$parent[] = $element;
}
}
return $parent;
}
$result = add_childs($arr);
print_r($result);
example : https://eval.in/745350

Answer 2

EDIT : I understood the question other way (parent attached to child)...
You have to iterate over users to look for every parent/child pairing.
<?php
$users = [
0 => ['id'=> 1, 'name' => 'A', 'parent_id' => null],
1 => ['id'=> 2, 'name' => 'B', 'parent_id' => 1],
2 => ['id'=> 3, 'name' => 'C', 'parent_id' => 2],
3 => ['id'=> 4, 'name' => 'D', 'parent_id' => 2],
3 => ['id'=> 4, 'name' => 'E', 'parent_id' => 4]
];
foreach($users as $user){
foreach($users as &$parent){
if($user['parent_id'] == $parent['id']){
$parent['children'][] = $user;
}
}
}
var_dump($users);
?>