添加不同的截距的垂直线为在GGPLOT2每个面板(Add a vertical line with

I'm using ggplot2 to create panels of histograms, and I'd like to be able to add a vertical line at the mean of each group. But geom_vline() uses the same intercept for each panel (i.e. the global mean):

require("ggplot2")
# setup some sample data
N <- 1000
cat1 <- sample(c("a","b","c"), N, replace=T)
cat2 <- sample(c("x","y","z"), N, replace=T)
val <- rnorm(N) + as.numeric(factor(cat1)) + as.numeric(factor(cat2))
df <- data.frame(cat1, cat2, val)

# draws a single histogram with vline at mean
qplot(val, data=df, geom="histogram", binwidth=0.2) + 
  geom_vline(xintercept=mean(val), color="red")

# draws panel of histograms with vlines at global mean
qplot(val, data=df, geom="histogram", binwidth=0.2, facets=cat1~cat2) + 
  geom_vline(xintercept=mean(val), color="red")

How can I get it to use each panel's group mean as the x-intercept? (Bonus points if you can also add a text label by the line with the value of the mean.)

Answer 1:

一种方法是构建data.frame与前手的平均值。

library(reshape)
dfs <- recast(data.frame(cat1, cat2, val), cat1+cat2~variable, fun.aggregate=mean)
qplot(val, data=df, geom="histogram", binwidth=0.2, facets=cat1~cat2) + geom_vline(data=dfs, aes(xintercept=val), colour="red") + geom_text(data=dfs, aes(x=val+1, y=1, label=round(val,1)), size=4, colour="red")

Answer 2:

我想这是@爱德华的一个改造真的，但在一行。

ggplot(df) + geom_histogram(mapping=aes(x=val)) 
  + geom_vline(data=aggregate(df[3], df[c(1,2)], mean), 
      mapping=aes(xintercept=val), color="red") 
  + facet_grid(cat1~cat2)

替代文字http://www.imagechicken.com/uploads/1264782634003683000.png

或使用plyr （ require(plyr)由ggplot，哈德利的作者的软件包）：

ggplot(df) + geom_histogram(mapping=aes(x=val)) 
  + geom_vline(data=ddply(df, cat1~cat2, numcolwise(mean)), 
      mapping=aes(xintercept=val), color="red") 
  + facet_grid(cat1~cat2)

看来不令人满意的是U电源没有切断的面，我不知道为什么。

文章来源: Add a vertical line with different intercept for each panel in ggplot2