- print_r: documentation ( source)
<?php
$first = ['01-1970' => 0.00, '03-2019' => 4350.00, '05-2019' => 150.00, '06-2019' => 50.00];
$second = ['03-2019' => 0.00, '04-2019' => 0.00, '06-2019' => 34.83];
$result = [];
foreach ([$first, $second] as $a) {
foreach ($a as $k=>$v) {
if (!isset($result[$k]))
$result[$k] = 0;
$result[$k] += $v;
}
}
print_r($result);