Align legend text in ggplot

Question

I find it difficult to combine the text of the legend on the left.

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") 

With this code, alignment is automatically left

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

However, with the following alignment is the center.

 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]))) 

How could I achieve left alignment with the last script?

Answer 1

You need to specify legend.text.align in theme() :

 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) 

Alternatively, try using bquote instead of expression , and the default alignment is the default. I don't know why just using expression changes the alignment to the right ...

 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])))