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<?php $items = array( (object) array('id' => 1, 'parent_id' => 0), (object) array('id' => 2, 'parent_id' => 0), (object) array('id' => 3, 'parent_id' => 0), (object) array('id' => 4, 'parent_id' => 1), (object) array('id' => 5, 'parent_id' => 1), (object) array('id' => 6, 'parent_id' => 2), ); function buildTree($items) { $childs = array(); foreach($items as $item) $childs[$item->parent_id][] = $item; foreach($items as $item) if (isset($childs[$item->id])) $item->childs = $childs[$item->id]; return $childs[0]; } $tree = buildTree($items); print_r($tree);
Output for 5.0.0 - 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29, 5.4.0 - 5.4.45, 5.5.0 - 5.5.14, 5.5.16 - 5.5.38, 5.6.0 - 5.6.32, 5.6.34 - 5.6.40, 7.0.0 - 7.0.9, 7.0.11, 7.0.13 - 7.0.33, 7.1.0 - 7.1.17, 7.1.19 - 7.1.33, 7.2.0 - 7.2.26, 7.3.0 - 7.3.13, 7.4.0 - 7.4.1, 8.1.28, 8.2.15 - 8.2.18, 8.3.2 - 8.3.6
Array ( [0] => stdClass Object ( [id] => 1 [parent_id] => 0 [childs] => Array ( [0] => stdClass Object ( [id] => 4 [parent_id] => 1 ) [1] => stdClass Object ( [id] => 5 [parent_id] => 1 ) ) ) [1] => stdClass Object ( [id] => 2 [parent_id] => 0 [childs] => Array ( [0] => stdClass Object ( [id] => 6 [parent_id] => 2 ) ) ) [2] => stdClass Object ( [id] => 3 [parent_id] => 0 ) )
Output for 5.5.15, 5.6.33, 7.0.10, 7.0.12, 7.1.18

Process exited with code 137.
Output for 4.3.0 - 4.3.11, 4.4.0 - 4.4.9
Array ( [0] => stdClass Object ( [id] => 1 [parent_id] => 0 ) [1] => stdClass Object ( [id] => 2 [parent_id] => 0 ) [2] => stdClass Object ( [id] => 3 [parent_id] => 0 ) )

preferences:
209.6 ms | 402 KiB | 335 Q