Plotting Expression in Legend

[Gokul Wimalanathan]

I was trying to figure out how to evaluate expressions on ggplot2 legend labels. 

I could not evaluate the expressions which are labels of factors with any build in parameter or function, and I had to use a simple function to get it done in the end, and the code I used to evaluate the expressions are given below.

library("data.table")

library("ggplot2")

variable=rep(c("fscore","cm_sq","co2"),1)

value=rnorm(n = 3,1,1)

tmp_dt <- data.table(variable,value)

tmp_dt[,variable:=factor(variable,levels=c("fscore","cm_sq","co2"),labels = c("F[1]","cm^2","CO[2]"),ordered = T)]

parse_expr <- function(x){

    return(parse(text= x))

}

p <- ggplot(tmp_dt,aes(x=variable,y=value,fill=variable))

p <- p + geom_bar(stat="identity") + scale_fill_brewer(type="qual",palette = 1,labels=parse_expr)

p <- p + scale_x_discrete(labels=parse_expr)

p

I was wondering if there was a parameter in ggplot2 that already exists that would do this for me?

Thanks