PHP合并多维数组和sum值的2个数组

$array1 = array(
    'a' => array('apple', 'banana'),
    'b' => array('orange', 'peach')
);

$array2 = array(
    'a' => array('grape'),
    'b' => array('watermelon')
);

$mergedArray = array_merge_recursive($array1, $array2);

print_r($mergedArray);

Array
(
    [a] => Array
        (
            [0] => apple
            [1] => banana
            [2] => grape
        )

    [b] => Array
        (
            [0] => orange
            [1] => peach
            [2] => watermelon
        )

)

$sumArray = array(
    'a' => array(1, 2, 3),
    'b' => array(4, 5, 6)
);

$sum = array_sum($sumArray);

echo $sum;

21