根据数据帧另一列中的计数向ggplot boxplot添加计数

Question

df2<-data.frame(id=c("a","f","f","b","b","c","c","c","d","d","",""),
                var=c(12,20,15,18,10,30,5,8,5,5,3,5),
                group=c(rep("group1", times=5), rep("group2", times=5), rep("",times=2)))


give.n <- function(x){
  return(c(y = max(x)+1, label = length(x)))
}
ggplot(data=subset(df2, id != ""), aes(x = reorder(group, -var), y = var)) +
  geom_boxplot()+
  stat_summary(fun.data = give.n, geom = "text", 
               position = position_jitter(height=1, width = 0))+
  theme(axis.text.x = element_text(angle = 90, hjust = 1, size=11, vjust = -.005))+
  ggtitle("Title")+
  xlab("")+
  ylab("value")

在上面的图表中，我想要计算＆＃39; var＆＃39;中的唯一变量。列在＆＃39; df2＆＃39;。因此，在结果图中，group1有3个，group2在boxplot上面有2个。我相信答案在于标签=＆＃39;但是，在函数中，我无法正确指定我想要的内容。 想法？