3v4l.org

run code in 300+ PHP versions simultaneously
<?php $arr = array( 2 => 'John', 21 => 'John', 32 => 'Joe', 42 => 'John', 23 => 'Joe', 62 => 'John', 25 => 'Joe', ); $flipped = []; foreach($arr AS $key => $value) { $flipped[$value][] = $key; } print_r($flipped);
Output for 5.5.0 - 5.5.36, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.31, 8.2.0 - 8.2.26, 8.3.0 - 8.3.14, 8.4.1
Array ( [John] => Array ( [0] => 2 [1] => 21 [2] => 42 [3] => 62 ) [Joe] => Array ( [0] => 32 [1] => 23 [2] => 25 ) )
preferences:
79.78 ms | 408 KiB | 5 Q