Online PHP editor | refs for OBh3k

<?php declare(strict_types=1); $items = [ (object)['id' => 1, 'parentId' => 0, 'name' => "foo"], (object)['id' => 2, 'parentId' => 1, 'name' => "bar"], (object)['id' => 3, 'parentId' => 1, 'name' => "qux"], (object)['id' => 4, 'parentId' => 3, 'name' => "zip"], (object)['id' => 5, 'parentId' => 4, 'name' => "baz"] ]; $itemsById = []; foreach ($items as $item) { $itemsById[$item->id] = $item; } // --- foreach ($itemsById as $id => $item) { $itemsById[$item->parentId]->children[] = $item; } var_dump($itemsById);