如何合并aes()和aes_string()选项 [英] How do I combine aes() and aes_string() options

问题描述

假设我有一个这样的情节

Let's say I have a plot like this

library(ggplot2)
ggplot(mtcars, aes(x=wt)) + ylab("") +
   geom_line(aes(y=mpg, color="one")) + 
   geom_line(aes(y=qsec, color="two")) + 
   scale_color_manual(name="Val", values=c(one="#105B63",two="#BD4932"))

在这里我绘制两条线，并为每条线指定一个颜色组.现在，假设我想动态地将变量名称指定为字符值，这意味着如果需要尝试，我将需要使用aes_string().

where I am plotting two lines and specifying a color group for each. Now let's say I want to specify the variables names dynamically as character values which means I'll need to use aes_string(). If I try

v1<-"mpg"
v2<-"qsec"
ggplot(mtcars, aes(x=wt)) + ylab("") +
   geom_line(aes_string(y=v1, color="one")) + 
   geom_line(aes_string(y=v2, color="two")) + 
   scale_color_manual(name="Val", values=c(one="#105B63",two="#BD4932"))

我得到了错误

Error in eval(expr, envir, enclos) : object 'one' not found

因为现在aes_string()试图解析颜色值，当我只想要文字字符值时.如果我尝试

because now aes_string() is trying to parse the color value when I just want a literal character value. And if I try

ggplot(mtcars, aes(x=wt)) + ylab("") +
   geom_line(aes_string(y=v1), aes(color="one")) + 
   geom_line(aes_string(y=v2), aes(color="two")) + 
   scale_color_manual(name="Val", values=c(one="#105B63",two="#BD4932"))

我知道

Error: ggplot2 doesn't know how to deal with data of class uneval

大概是因为该层不知道如何处理两个美学指令.

presumably because the layer doesn't know how to handle two aesthetic directives.

如何结合aes()和aes_string()美学，或者如何为aes_string()指定文字字符值?

How can I combine aes() and aes_string() aesthetics or how can I specify literal character values for aes_string()?

推荐答案

如果要在aes_string()中指定字符文字值，最简单的方法是使用shQuote()引用该值.例如

If you want to specify a character literal value in aes_string(), the easiest thing would be to use shQuote() to quote the value. For example

ggplot(mtcars, aes(x=wt)) + ylab("") +
   geom_line(aes_string(y=v1, color=shQuote("one"))) + 
   geom_line(aes_string(y=v2, color=shQuote("two"))) + 
   scale_color_manual(name="Val", values=c(one="#105B63",two="#BD4932"))

之所以起作用，是因为aes_string()实际上在每个参数值上运行parse(text=). shQuote()函数在字符值周围添加引号，以便在解析该值时，您可以返回一个字符值，而不是符号/名称.比较这两个电话

This works because aes_string() actually runs parse(text=) on each of the parameter values. The shQuote() function adds quotes around your character value so that when you parse the value, you get a character value back rather than a symbol/name. Compare these two calls

class(parse(text="a")[[1]])
# [1] "name"
class(parse(text=shQuote("a"))[[1]])
# [1] "character"

或者，您可能会考虑合并aes()指令. aes()函数实际上只是返回具有uneval类的列表.我们可以定义一个函数来合并/合并这些列表.例如，我们可以定义加法

Alternatively, you might think of merging aes() directives. The aes() functions really just return a list with a class of uneval. We could define a function to combine/merge these list. For example we can define addition

`+.uneval` <- function(a,b) {
    `class<-`(modifyList(a,b), "uneval")
}

现在我们可以做

ggplot(mtcars, aes(x=wt)) + ylab("") +
   geom_line(aes_string(y=v1) + aes(color="one")) + 
   geom_line(aes_string(y=v2) + aes(color="two")) + 
   scale_color_manual(name="Val", values=c(one="#105B63",two="#BD4932"))

这篇关于如何合并aes()和aes_string()选项的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！