我正在使用ggplot2创建直方图面板,并希望能够在每个组的均值处添加一条竖线。但是geom_vline()对于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")
如何让它使用每个面板的组均值作为x轴截距?(如果您还可以在线条旁边添加一个文本标签,显示均值的值,则可获得额外的积分。)