R: how to construct a mathematical expression from a character object?

Question

In R, I'm wanting to create a graph with x axis label expression(varname), where varname is a character object. For example:

varname <- "beta[1]"
hist(rnorm(20),xlab=expression(varname))

But that gives me a graph with xlab="varname" rather than xlab=expression(beta[1]). How to I convince expression() to evaluate the variable?

Answer 1

you can do by

hist(rnorm(20),xlab=parse(text=varname))