如何使geom_vline遵守facet_wrap？

Question

我已经查找了一些资料，但是没有找到答案。我想做一个加权的geom_bar图，上面覆盖着一条竖直线，显示每个facet的加权平均值。但我无法实现这一点。竖直线似乎只对所有facets应用单个值。

require('ggplot2')
require('plyr')

# data vectors
panel <- c("A","A","A","A","A","A","B","B","B","B","B","B","B","B","B","B")
instrument <-c("V1","V2","V1","V1","V1","V2","V1","V1","V2","V1","V1","V2","V1","V1","V2","V1")
cost <- c(1,4,1.5,1,4,4,1,2,1.5,1,2,1.5,2,1.5,1,2)
sensitivity <- c(3,5,2,5,5,1,1,2,3,4,3,2,1,3,1,2)

# put an initial data frame together
mydata <- data.frame(panel, instrument, cost, sensitivity)

# add a "contribution to" vector to the data frame: contribution of each instrument
# to the panel's weighted average sensitivity.
myfunc <- function(cost, sensitivity) {
  return(cost*sensitivity/sum(cost))
}
mydata <- ddply(mydata, .(panel), transform, contrib=myfunc(cost, sensitivity))

# two views of each panels weighted average; should be the same numbers either way
ddply(mydata, c("panel"), summarize, wavg=weighted.mean(sensitivity, cost))
ddply(mydata, c("panel"), summarize, wavg2=sum(contrib))

# plot where each panel is getting its overall cost-weighted sensitivity from. Also
# put each panel's weighted average on the plot as a simple vertical line.
#
# PROBLEM! I don't know how to get geom_vline to honor the facet breakdown. It
#          seems to be computing it overall the data and showing the resulting
#          value identically in each facet plot.
ggplot(mydata, aes(x=sensitivity, weight=contrib)) +
  geom_bar(binwidth=1) +
  geom_vline(xintercept=sum(contrib)) +
  facet_wrap(~ panel) +
  ylab("contrib")

- user1443547

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我之前遇到了一个问题，因为我的x轴是一个因子变量，所以它没有正常显示。花了一些时间才明白原因。 - Ufos

Answer 1

如果你传入预处理后的数据，它似乎可以正常工作：

ggplot(mydata, aes(x=sensitivity, weight=contrib)) +
  geom_bar(binwidth=1) +
  geom_vline(data = ddply(mydata, "panel", summarize, wavg = sum(contrib)), aes(xintercept=wavg)) +
  facet_wrap(~ panel) +
  ylab("contrib") +
  theme_bw()

- Chase

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不错的解决方案，但问题评估不正确。问题有两个方面：（1）数据未按面板汇总，而是一个常数；（2）sum(contrib)未传递到mapping函数(aes)。 - o_v

Answer 2

如果有人想使用dplyr和facet_wrap进行示例，可以参考以下内容。

library(dplyr)
library(ggplot2)

df1 <- mutate(iris, Big.Petal = Petal.Length > 4)
df2 <- df1 %>%
  group_by(Species, Big.Petal) %>%
  summarise(Mean.SL = mean(Sepal.Length))

ggplot() +
  geom_histogram(data = df1, aes(x = Sepal.Length, y = ..density..)) +
  geom_vline(data = df2, mapping = aes(xintercept = Mean.SL)) +
  facet_wrap(Species ~ Big.Petal) 

- R.Sanchez

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好的回答。那么在每个图中是否可以做出>1行？这样xintercept将由多列组成。 - JdP

Answer 3

 vlines <- ddply(mydata, .(panel), summarize, sumc = sum(contrib))
 ggplot(merge(mydata, vlines), aes(sensitivity, weight = contrib)) + 
 geom_bar(binwidth = 1) + geom_vline(aes(xintercept = sumc)) + 
 facet_wrap(~panel) + ylab("contrib")

- Maiasaura