3v4l.org

run code in 300+ PHP versions simultaneously
<?php $array_list= array("Jan 2016"=>2, "Feb 2016"=>4, "Mar 2016"=>2,"Apr 2016"=>0, "Jan 2017"=>9,"Feb 2017"=>2,"Mar 2017"=>5,"Jan 2018"=>4,"Feb 2018"=>6); foreach(array_keys($array_list) as $key){ $years[] = explode(" ", $key)[1]; } foreach(array_unique($years) as $year){ $res[$year] = array_sum(array_intersect_key(array_values($array_list), array_intersect($years, [$year]))); } var_dump($res);
Output for 7.1.0 - 7.1.25, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.25, 8.4.1 - 8.4.12
array(3) { [2016]=> int(8) [2017]=> int(16) [2018]=> int(10) }
preferences:
144.89 ms | 407 KiB | 5 Q