如何在多维数组中合并重复的键？

function mergeDuplicateKeys($array) {
    $result = array();

    foreach ($array as $key => $value) {
        if (is_array($value)) {
            // 递归调用合并重复的键
            $value = mergeDuplicateKeys($value);
        }

        if (isset($result[$key])) {
            // 如果已存在相同的键，合并值
            if (is_array($result[$key]) && is_array($value)) {
                $result[$key] = mergeDuplicateKeys(array_merge($result[$key], $value));
            } else {
                $result[$key] = $result[$key] . ', ' . $value;
            }
        } else {
            // 如果不存在相同的键，添加到结果数组中
            $result[$key] = $value;
        }
    }

    return $result;
}

// 示例多维数组
$array = array(
    'key1' => 'value1',
    'key2' => array(
        'subkey1' => 'subvalue1',
        'subkey2' => 'subvalue2'
    ),
    'key3' => 'value3',
    'key4' => array(
        'subkey1' => 'subvalue3',
        'subkey2' => 'subvalue4'
    )
);

// 调用函数合并重复的键
$result = mergeDuplicateKeys($array);

// 输出结果
print_r($result);

Array
(
    [key1] => value1
    [key2] => Array
        (
            [subkey1] => subvalue1
            [subkey2] => subvalue2
        )
    [key3] => value3
    [key4] => Array
        (
            [subkey1] => subvalue3
            [subkey2] => subvalue4
        )
)