控制 ggplot2 中 facet_grid/facet_wrap 的顺序? [英] controlling order of facet_grid/facet_wrap in ggplot2?

问题描述

我正在使用 ggplot 中的 facet_wrap 和 facet_grid 进行绘图，例如:

I am plotting things using facet_wrap and facet_grid in ggplot, like:

ggplot(iris) + geom_histogram(aes(iris$Petal.Width)) + facet_grid(Species ~ .)

是否可以控制 Species 面板在图中的排列顺序?这可以在不更改 iris 数据帧或创建新数据帧的情况下完成吗?此处默认显示 setosa、versicolor、virginica，但我想要不同的顺序.谢谢.

Is it possible to control the order in which the Species panels are ordered in the plot? Can this be done without changing the iris dataframe or making a new one? The default here shows setosa, versicolor, virginica but I'd like a different order. thanks.

推荐答案

我认为我无法真正满足您的不制作新数据框"要求，但您可以即时创建新数据框:

I don't think I can really satisfy your "without making a new data frame" requirement, but you can create the new data frame on the fly:

ggplot(transform(iris,
      Species=factor(Species,levels=c("virginica","setosa","versicolor")))) + 
    geom_histogram(aes(Petal.Width))+ facet_grid(Species~.)

或者，在 tidyverse 成语中:

or, in tidyverse idiom:

iris %>%
   mutate(across(Species, factor, levels=c("virginica","setosa","versicolor"))) %>%
ggplot() + 
   geom_histogram(aes(Petal.Width))+ 
   facet_grid(Species~.)

我同意如果有另一种方法来控制它会很好，但是 ggplot 已经是一个非常强大(且复杂)的引擎......

I agree it would be nice if there were another way to control this, but ggplot is already a pretty powerful (and complicated) engine ...

请注意，(1) 数据集中的行的顺序与 (2) 因子的级别的顺序无关.#2 是 factor(...,levels=...) 变化的内容，以及 ggplot 用来确定构面顺序的内容.做#1(按指定顺序对数据框的行进行排序)是一个有趣的挑战.我想我实际上可以通过先做 #2 来实现这一点，然后使用 order() 或 arrange() 根据因子的数值进行排序:

Note that the order of (1) the rows in the data set is independent of the order of (2) the levels of the factor. #2 is what factor(...,levels=...) changes, and what ggplot looks at to determine the order of the facets. Doing #1 (sorting the rows of the data frame in a specified order) is an interesting challenge. I think I would actually achieve this by doing #2 first, and then using order() or arrange() to sort according to the numeric values of the factor:

neworder <- c("virginica","setosa","versicolor")
library(plyr)  ## or dplyr (transform -> mutate)
iris2 <- arrange(transform(iris,
             Species=factor(Species,levels=neworder)),Species)

如果不改变因子水平的顺序，我无法立即看到一种快速的方法(你可以这样做，然后相应地重置因子水平的顺序).

I can't immediately see a quick way to do this without changing the order of the factor levels (you could do it and then reset the order of the factor levels accordingly).

一般来说，R 中依赖于分类变量级别顺序的函数基于因子级别顺序，而不是数据集中行的顺序:上述答案更普遍.

In general, functions in R that depend on the order of levels of a categorical variable are based on factor level order, not the order of the rows in the dataset: the answer above applies more generally.

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