ggplot greek letter in label within for loop indices

Question

I need to add the theta greek letter in the x-axis label of this plot(s):

var=c("a", "b", "c")

df=data.frame(x=c(1:20),y=c(41:60))

df_plot=list()

for (i in 1:length(var)) {
  
  df_plot[[i]]=ggplot()+
  
  geom_line(data=df, aes(x=x, y=y))+
  xlab(paste("theta ", var[i]))

}

How can I do it?

If I use expression() I get the letter but not the index i.

Answer 1

Using bquote you could do:

Note: Instead of using a for loop I switched to lapply (and would suggest to so) as sooner or later you will run in issues related to tidy evaluation when using a for loop with ggplot. And there are plenty of questions on SO related to that. (:

var <- c("a", "b", "c")

df <- data.frame(x = c(1:20), y = c(41:60))

library(ggplot2)

lapply(var, function(x) {
  ggplot() +
    geom_line(data = df, aes(x = x, y = y)) +
    xlab(bquote(theta*.(x)))
})
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