Online PHP editor | refs for DJCV3

<?php $array = [ ['id' => 15, 'parent' => 12], ['id' => 10, 'parent' => 12], ['id' => 12, 'parent' => 12], ['id' => 17, 'parent' => 12], ['id' => 21, 'parent' => 15], ['id' => 13, 'parent' => 15], ['id' => 15, 'parent' => 15], ['id' => 25, 'parent' => 15], ['id' => 7, 'parent' => 7], ['id' => 18, 'parent' => 7], ['id' => 4, 'parent' => 7], ['id' => 1, 'parent' => 3], ['id' => 5, 'parent' => 5], ['id' => 2, 'parent' => 7], ]; usort( $array, fn($a, $b) => [$a['parent'], $a['id'] !== $a['parent'], $a['id']] <=> [$b['parent'], $b['id'] !== $b['parent'], $b['id']] ); var_export($array);