r - 在 ggplot 中对齐图例文本

Question

我很难将图例文本向左对齐。

library(ggplot2)
library(reshape2)
o3<- rnorm(1827, 50, 10)
NO2<- rnorm(1827, 35, 7)
NOx<- rnorm(1827, 45, 10)
pm25<- rnorm(1827, 15, 4)
date<-seq(as.Date('2000-01-01'),as.Date('2004-12-31'),by = 1)
df<-data.frame(date,o3,NO2,NOx,pm25)
meltdf <- melt(df,id="date")

使用此代码，对齐方式会自动向左

ggplot(meltdf, aes(x = date, y = value, colour =variable)) + geom_smooth() + stat_smooth(method = "gam")

但是，下面的对齐方式是居中。

ggplot(meltdf, aes(x = date, y = value, colour =variable)) + 
      geom_smooth() + stat_smooth(method = "gam") +
      scale_color_discrete(name="Pollutant" ,labels = c(expression(O[3]),
                                expression(NO[2]),
                                expression(NO[x]),
                                expression(PM[2.5]))) 

如何实现与上一个脚本的左对齐？

Answer 1

您需要在theme()中指定legend.text.align:

ggplot(meltdf, aes(x = date, y = value, colour =variable)) + 
geom_smooth() + 
stat_smooth(method = "gam") +
scale_color_discrete(name="Pollutant", 
    labels = c(expression(O[3]),
               expression(NO[2]),
               expression(NO[x]),
               expression(PM[2.5]))) +
theme(legend.text.align = 0)

或者，尝试使用bquote而不是表达式，并且会发生默认的左对齐。我不知道为什么只使用表达式就会将对齐方式更改为右侧...

ggplot(meltdf, aes(x = date, y = value, colour =variable)) + 
geom_smooth() + 
stat_smooth(method = "gam") +
scale_color_discrete(name="Pollutant", 
    labels = c(bquote(O[3]),
               bquote(NO[2]),
               bquote(NO[x]),
               bquote(PM[2.5])))