如何在 ggplot 中的 aes() 和本地 geom_xxx() 中手动设置颜色*有条件*？

Question

我正在尝试创建一个函数，该函数可以采用单个组或多个组，同时使用单个 colour 参数。但是，在全局（aes()）和本地（geom_smooth()）中指定colour 似乎存在问题。看起来aes() 不接受colour=NULL 或者只是留空colour=。

无组情节（作品）

scatterfunction <- function (Data=mtcars,Predictor=mtcars$wt,Response=mtcars$mpg,what.Colour="purple") {
  library(ggplot2)
  ggplot(Data,aes(x=Predictor,y=Response)) +
    geom_smooth(method="lm",colour=what.Colour)
}
scatterfunction()

与团体一起策划（作品）

groupscatterfunction <- function (Data=mtcars,Predictor=mtcars$wt,Response=mtcars$mpg,Group.variable=factor(mtcars$cyl),what.Colour=c("purple", "yellow", "brown")) {
  library(ggplot2)
  ggplot(Data,aes(x=Predictor,y=Response,colour=Group.variable)) +
    geom_smooth(method="lm") +
    scale_color_manual(values=what.Colour)
}
groupscatterfunction()

不带组的情节，有条件的（has.Groups=F 时有效）

conditionalscatterfunction <- function (Data=mtcars,Predictor=mtcars$wt,Response=mtcars$mpg,Group.variable=factor(mtcars$cyl),has.Groups=F,what.Colour="purple") {
  library(ggplot2)
  ggplot(Data,aes(x=Predictor,y=Response,colour= if(has.Groups==T) {Group.variable})) +
    geom_smooth(method="lm",colour= if(has.Groups==F){what.Colour}) +
    if (has.Groups==T) {scale_color_manual(values=what.Colour)}
}
conditionalscatterfunction()

按组绘制，有条件（has.Groups=T 时不起作用）

conditionalscatterfunction(Data = mtcars,
                           Predictor = mtcars$wt,
                           Response = mtcars$mpg,
                           has.Groups = TRUE,
                           Group.variable = factor(mtcars$cyl),
                           what.Colour = c("purple", "yellow", "brown"))

Error: Aesthetics must be either length 1 or the same as the data (80): colour

使用替代 switch() 语句以前对我有用，但在这里不行：

conditionalscatterfunction <- function (Data=mtcars,Predictor=mtcars$wt,Response=mtcars$mpg,Group.variable=factor(mtcars$cyl),has.Groups=T,what.Colour=c("purple", "yellow", "brown")) {
  library(ggplot2)
  ggplot(Data,aes(x=Predictor,y=Response,colour= switch(has.Groups, Group.variable))) +
    geom_smooth(method="lm",colour= if(has.Groups==F){what.Colour}) +
    if (has.Groups==T) {scale_color_manual(values=what.Colour)}
}
conditionalscatterfunction()

Error: Aesthetics must be either length 1 or the same as the data (80): colour

似乎只要我在aesthetics() 中添加“colour=”语句，无论是留空还是= NULL，都会出现此错误。那么当没有显式调用时它的默认值是什么？

我宁愿避免再次重复整个调用，因为geom_points()、geom_shape() 等也有这个问题，我需要为每个元素组合重复它...

问题：我该如何解决这个问题？

Answer 1

有很多方法可以给这只猫剥皮，但一个简单的方法是使用if {} else {} 预先定义geom_smooth。例如：

conditionalscatterfunction <- function (Data, Predictor, Response, Group.variable, col = c("purple", "yellow", "brown")) {
  require(ggplot2)

  if (missing(Group.variable)) {
    smooth <- geom_smooth(method = "lm", color = col[1])
  } else {
    smooth <- geom_smooth(aes(color = {{Group.variable}}), method = "lm")
  }

  ggplot(Data, aes(x = {{Predictor}},y = {{Response}})) +
    smooth +
    scale_color_manual(values = col)
}

conditionalscatterfunction(mtcars, wt, mpg)
conditionalscatterfunction(mtcars, wt, mpg, factor(cyl))

两者都可以正常工作。