在ggplot2中按组修改alpha值

Question

我想改变alpha刻度，现在我认为它从0到1。 我想把它从0.2到0.5左右。因为这样我们就不能很好地看到事件填充颜色.M＆＃34;太暗了，M1太亮......

这是数据库信息：

> str(st2)

'data.frame':   24 obs. of  6 variables:
 $ Outcome   : Factor w/ 4 levels "LGiT","LGuT",..: 3 3 3 1 1 1 2 2 2 4 ...
 $ Event     : Factor w/ 3 levels "Event 1","Event 2",..: 1 2 3 1 2 3 1 2 3 1 ...
 $ Percentage: num  10.31 8.25 81.44 12.77 15.32 ...
 $ Method    : Factor w/ 2 levels "M1","M2": 1 1 1 1 1 1 1 1 1 1 ...
 $ Cohort    : Factor w/ 1 level "Cohort 1": 1 1 1 1 1 1 1 1 1 1 ...
 $ label     : chr  "10%" "8%" "81%" "13%" ...
 $ sum       : chr  "100.00%" "100.00%" "100.00%" "100.00%" ...

这是剧情代码：

p7<-ggplot(st2, aes(x = factor(st2$Outcome:st2$Method), y = st2$Percentage,  
                fill = st2$Event, group=st2$Event)) +
  geom_bar(aes(alpha=st2$Method),position = position_stack(), stat = "identity", width = .7, colour="black") +
  geom_text(aes(label = st2$label), position = position_stack(vjust = 0.5),size = 4) + coord_flip() 


p8<-p7+labs(x="Outcome", y="Percentage Values", fill="Legend")+ scale_fill_grey(start=1, end=0.8)+ theme(axis.text=element_text(size=15), axis.title=element_text(size=17, face="bold"), legend.title=element_text(size=13), legend.text=element_text(size=12))


p8+theme_bw() + theme(panel.border = element_blank(), panel.grid.major = element_blank(), panel.grid.minor = element_blank(), axis.line = element_line(colour = "black"))

这是我的情节：

我已尝试添加

scale_alpha(limits=c(0.2,0.5))

但它不起作用：错误：提供给连续刻度的离散值

谢谢！