Get sum of multiple array values with same keys.

sumArrays.php

<?php
function sumArrays (array ...$a): array
{
    foreach ($a as $arr) {
        if (!empty($merged)){
            $arr = array_flip(array_keys($merged+$arr));
        }
        $merged = $arr;
    }
    
    $result = array_fill_keys(array_flip($merged),0);
    
    foreach ($a as $arr) {
        foreach ($arr as $k=>$v) {
            $result[$k] += $v;
        }
    }
    
    return $result;
}


$z = sumArrays(['1a'=>10,'2a'=>20],['2a'=>30,'3a'=>40],['3a'=>50,'4a'=>60],['a'=>2]);
/*
Array
(
    [1a] => 10
    [2a] => 50
    [3a] => 90
    [4a] => 60
    [a] => 2
)
*/