使用stat_summary通过观察值的数量对图进行注释 [英] Use stat_summary to annotate plot with number of observations

问题描述

如何使用 stat_summary 来为 n = x 标记一个图，其中 x 一个变量？以下是所需输出的示例：

How can I use stat_summary to label a plot with n = x where is x a variable? Here's an example of the desired output:

我可以用这个效率很低的代码来做上面的绘图：

I can make that above plot with this rather inefficient code:

nlabels <- sapply(1:length(unique(mtcars$cyl)), function(i) as.vector(t(as.data.frame(table(mtcars$cyl))[,2][[i]])))
ggplot(mtcars, aes(factor(cyl), mpg, label=rownames(mtcars))) +
  geom_boxplot(fill = "grey80", colour = "#3366FF") + 
  geom_text(aes(x = 1, y = median(mtcars$mpg[mtcars$cyl==sort(unique(mtcars$cyl))[1]]), label = paste0("n = ",nlabels[[1]]) )) +
  geom_text(aes(x = 2, y = median(mtcars$mpg[mtcars$cyl==sort(unique(mtcars$cyl))[2]]), label = paste0("n = ",nlabels[[2]]) )) +
  geom_text(aes(x = 3, y = median(mtcars$mpg[mtcars$cyl==sort(unique(mtcars$cyl))[3]]), label = paste0("n = ",nlabels[[3]]) )) 

这是这个问题的后续内容：如何在每个组中添加多个观察值并在ggplot2 boxplot中使用组均值？可以使用 stat_summary 以计算并显示观察次数，但我一直无法找到在 stat_summary n = 的方法$ c>输出。看起来像 stat_summary 可能是进行这种标记的最有效的方法，但也可以使用其他方法。

This is a follow up to this question: How to add a number of observations per group and use group mean in ggplot2 boxplot? where I can use stat_summary to calculate and display the number of observations, but I haven't been able to find a way to include n = in the stat_summary output. Seems like stat_summary might be the most efficient way to do this kind of labelling, but other methods are welcome.

推荐答案

您可以在 stat_summary（）中使用自己的函数。这里 n_fun 计算y值的位置为 median（），然后添加 label = ，其中包括 n = 和观测值的数量。使用 data.frame（）代替 c（）是很重要的，因为 paste0（ ）会产生字符，但 y 的值是数字，但是 c（）字符。然后在 stat_summary（）中使用此函数，并在 geom =text中使用。这将确保对于每个x值，位置和标签只能从这个级别的数据中获得。

You can make your own function to use inside the stat_summary(). Here n_fun calculate place of y value as median() and then add label= that consist of n= and number of observations. It is important to use data.frame() instead of c() because paste0() will produce character but y value is numeric, but c() would make both character. Then in stat_summary() use this function and geom="text". This will ensure that for each x value position and label is made only from this level's data.

n_fun <- function(x){
  return(data.frame(y = median(x), label = paste0("n = ",length(x))))
}

ggplot(mtcars, aes(factor(cyl), mpg, label=rownames(mtcars))) +
  geom_boxplot(fill = "grey80", colour = "#3366FF") + 
  stat_summary(fun.data = n_fun, geom = "text")

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