在ggplot2中为每个面板添加一条具有不同截距的垂直线

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):

我使用ggplot2来创建直方图面板，我希望能够在每个组的均值上添加一条垂直线。但是geom_vline()对每个面板使用相同的截距(即全局平均值):

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.)

我怎么能让它用每个面板的组均值作为x轴截距?(如果您还可以在一行中添加一个带有平均值的文本标签，则可获得加分。)

2 个解决方案

#1

One way is to construct the data.frame with the mean values before hand.

一种方法是用手边的平均值构造data.frame。

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")

#2

I guess this is a reworking of @eduardo's really, but in one line.

我猜这是对@eduardo的作品的改编，但在一行中。

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)

alt text http://www.imagechicken.com/uploads/1264782634003683000.png

alt文本http://www.imagechicken.com/uploads/1264782634003683000.png

or using plyr (require(plyr) a package by the author of ggplot, Hadley):

或者使用plyr(要求(plyr)一个由ggplot作者Hadley编写的包):

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)

It seems unsatisfying that vline isn't cut on the facets, I'm not sure why.

我不知道为什么vline没有在切面上切割，这似乎不令人满意。

#1