您可以加入数据并使用 coalesce 选择非 NA 值.

You can join the data and use coalesce to select non-NA value.

library(dplyr)

x %>%
  left_join(y, by = 'Month') %>%
  mutate(Value = coalesce(Value.x, Value.y)) %>%
  select(names(x))

在基础 R 中，您可以merge 并使用 ifelse 选择非 NA 值

In base R, you can merge and use ifelse to select non-NA value

transform(merge(x, y, by = 'Month'), 
          Value = ifelse(is.na(Value.x), Value.y, Value.x))[names(x)]