R中的上标图例文本

Question

I am currently trying to superscript legend text in R similar to Latex. I have variables such as "xx", "xxx", "yy", and "zz" and am wondering if it is possible to automatically convert these to superscripts such as $x^2$ in Latex. I know of expression(paste0("x"^"2")) for ggplot but it is unclear how to implement it or change the text automatically.

matrix <- matrix(rexp(200, rate=.1), ncol=20)
df <- data.frame(matrix)
variables <- c("x","y","z","xx","xy","yy","xz","yz","zz","xxx")

df$variables <- variables

new.df <- melt(df, id.vars="variables")

ggplot(new.df, aes(x = variable, y = value, col=variables, group = variables))+
  geom_point()+
  geom_line()

Answer 1

you still have to use expression()

EDIT: you can use rlang 's parse_exprs() with eval to autmatically convert you vars into expression:

#variables_ex <- rep(expression(paste(x^x[y])),10)
##EDIT: universal solution:

library(rlang)

variables <- c("x","y","z","xx","xy","yy","xz","yz","zz","xxx")

exlabel<-paste(variables,"^x[y]",sep="")


ggplot(new.df, aes(x = variable, y = value, col=variables, group = variables))+
  geom_point()+
  geom_line()+ labs(x = variables_ex)+
  scale_color_discrete(name = "Superlegend", labels= eval(parse_exprs(exlabel)))+
  theme( legend.text = element_text(color = "red"))