ggplot 中的特殊变量(..count..、..density.. 等) [英] Special variables in ggplot (..count.., ..density.., etc.)

问题描述

考虑以下几行.

p <- ggplot(mpg, aes(x=factor(cyl), y=..count..))

p + geom_histogram()   
p + stat_summary(fun.y=identity, geom='bar')

理论上，最后两个应该产生相同的情节.在实践中，stat_summary 失败并抱怨缺少所需的 y 美学.

In theory, the last two should produce the same plot. In practice, stat_summary fails and complains that the required y aesthetic is missing.

为什么我不能在 stat_summary 中使用 ..count..?我在文档中找不到任何关于如何使用这些变量的信息.

Why can't I use ..count.. in stat_summary? I can't find anywhere in the docs information about how to use these variables.

推荐答案

扩展@joran 的评论，ggplot 中的特殊变量周围有双句点 (..count.., ..密度.. 等)由原始数据集的统计转换返回.那些特定的由 stat_bin 返回，它被 geom_histogram 隐式调用(注意在文档中 stat 参数的默认值是 "bin").您的第二个示例调用了一个不同的 stat 函数，该函数不会创建名为 ..count.. 的变量.您可以使用

Expanding @joran's comment, the special variables in ggplot with double periods around them (..count.., ..density.., etc.) are returned by a stat transformation of the original data set. Those particular ones are returned by stat_bin which is implicitly called by geom_histogram (note in the documentation that the default value of the stat argument is "bin"). Your second example calls a different stat function which does not create a variable named ..count... You can get the same graph with

p + geom_bar(stat="bin")

在较新版本的 ggplot2 中，还可以使用 stat 函数代替封闭的 ..，因此 aes(y = ..count..) 变成 aes(y = stat(count)).

In newer versions of ggplot2, one can also use the stat function instead of the enclosing .., so aes(y = ..count..) becomes aes(y = stat(count)).

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