Latex and variables in plot label in R?

Question

How do I use variables in Latex expressions in R?

For example:

plot(X, Y, main=expression(R^2))

Will put R with a nice superscripted 2

Answer 1

Another variation on @Joris' theme is substitute(). You give substitute() an expression and an environment or list within which to evaluate the expression. Passing a list is usually easiest, especially for jobs such as the one posed here.

plot(X,Y, main = substitute(R^2 : a, list(a = a)))

We can see why this works, by looking solely at the substitute() call:

> substitute(R^2 : a, list(a = a))
R^2:0.8

The a in the expression is replace with the value of a in the list.