Online PHP editor | output for kRVDc

<?php $collection = [ [1 => 10.0, 2 => 20.0, 3 => 50.0, 4 => 80.0, 5 => 100.0], [3 => 20.0, 5 => 20.0, 6 => 100.0, 7 => 10.0], [1 => 30.0, 3 => 30.0, 5 => 10.0, 8 => 10.0] ]; var_export( array_reduce( array_keys( array_intersect_ukey( ...array_merge( $collection, [fn($a, $b) => $a <=> $b] ) ) ), fn($result, $k) => $result + [$k => array_sum(array_column($collection, $k)) / count($collection)], [] ) );