ggplot geom_bar:aes(组= 1)的含义 [英] ggplot geom_bar: meaning of aes(group = 1)

问题描述

我正在r4ds.had.co.nz的3.7节中学习 geom_bar .我运行这样的代码:

I am learning geom_bar on section 3.7 of r4ds.had.co.nz. I run a code like this:

library(ggplot2)
ggplot(data = diamonds) + geom_bar(mapping = aes(x = cut, y = ..prop.., group = 1))

然后我有这个情节:

Then I have this plot:

要点是，如果我排除组= 1"部分:

The point is, if I exclude the "group = 1" part:

library(ggplot2)
ggplot(data = diamonds) + geom_bar(mapping = aes(x = cut, y = ..prop..))

情节将是错误的，

但是，如果我将group = 1替换为group = 2或group ="x"，则该图看起来仍然正确.所以我不太了解group = 1的含义以及如何使用它.

But if I replace group = 1 by group = 2 or group = "x", the plot still looks correct. So I don't quite understand the meaning of group = 1 here and how to use it.

推荐答案

group="whatever"是一个虚拟"分组，用于覆盖默认行为，默认行为是(此处)按cut分组，通常是按x变量. geom_bar的默认值是按x变量分组，以便分别计算x变量每个级别中的行数.例如，在这里，默认设置是geom_bar返回cut等于"Fair"，"Good"等的行数.

group="whatever" is a "dummy" grouping to override the default behavior, which (here) is to group by cut and in general is to group by the x variable. The default for geom_bar is to group by the x variable in order to separately count the number of rows in each level of the x variable. For example, here, the default would be for geom_bar to return the number of rows with cut equal to "Fair", "Good", etc.

但是，如果我们需要比例，那么我们需要一起考虑cut的所有级别.在第二个图中，首先将数据按cut分组，因此分别单独考虑cut的每个级别.公平中公平的比例为100％，商品中良好等的比例也是100％.group=1(或group="x"等)可防止这种情况，因此每个级别的切割比例将相对于所有削减水平.

However, if we want proportions, then we need to consider all levels of cut together. In the second plot, the data are first grouped by cut, so each level of cut is considered separately. The proportion of Fair in Fair is 100%, as is the proportion of Good in Good, etc. group=1 (or group="x", etc.) prevents this, so that the proportions of each level of cut will be relative to all levels of cut.

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