在ggplot2的堆叠条形图的顶部显示每个组的总计（总和）值

我使用此代码制作了以下堆积条形图：

library(ggplot2)
library(dplyr)

Year      <- c(rep(c("2006", "2007", "2008", "2009"), each = 4))
Category  <- c(rep(c("A", "B", "C", "D"), times = 4))
Frequency <- c(168, 259, 226, 340, 216, 431, 319, 368, 423, 645, 234, 685, 166, 467, 274, 251)
Data      <- data.frame(Year, Category, Frequency)

Data2 <-Data%>%
  group_by(Year, Category)%>%
    summarise(Sum_grp = sum(Frequency))

Data3 <-transform(Data2, Pos = ave(Frequency, Year, FUN = cumsum) - Frequency / 2)

ggplot(Data3, aes(Year, Frequency, group=Category,fill = Category))+
  geom_bar(stat="identity")+
  geom_text(aes(label = Frequency,y=Pos), size = 3) 

现在，我想将每个组的总和添加到每个小节的顶部，但是我不知道如何。

有人可以帮我吗？

非常感谢！！！！！