Is there a clean way to accomplish the following without writing an ugly bunch of for loops and logic blocks?

PHP Code:
<?php

//INPUT
$aRaw = [
    [
'in' => [1,2,3], 'out' =>[4,5,6]],
    [
'in' => [7,8,9], 'out' =>[1,2,3]]
];

//DESIRED OUTPUT
$aSum = ['in' => [8,10,12], 'out' =>[5,7,9]];

?>
$aN is a factor, so there may only be one set in $aRaw or there may be 5+

Thank you =)