3v4l.org

run code in 300+ PHP versions simultaneously
<?php $array = ["Ripe Mango"=>"Yellow", "Strawberry"=>"Red", "Lemon"=>"Yellow"]; var_export( array_reduce( array_keys($array), fn($result, $key) => array_merge_recursive($result, [$array[$key] => [$key]]), [] ) );
Output for 8.0.1 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.26, 8.4.1 - 8.4.13
array ( 'Yellow' => array ( 0 => 'Ripe Mango', 1 => 'Lemon', ), 'Red' => array ( 0 => 'Strawberry', ), )

preferences:
59.08 ms | 407 KiB | 5 Q