3v4l.org

run code in 300+ PHP versions simultaneously
<?php $a = [ 'a' => 0, 'b' => 0, 'c' => 1 ]; $result = []; foreach ($a as $result[$v][] => $v); var_export($result);
Output for 8.1.0 - 8.1.28, 8.2.0 - 8.2.19, 8.3.0 - 8.3.7
array ( 0 => array ( 0 => 'a', 1 => 'b', ), 1 => array ( 0 => 'c', ), )

preferences:
81.61 ms | 402 KiB | 62 Q