r - Use a variable within a plotmath expression

Question

I'm trying to place the results of a regression (i.e., R2) in a graph, but can't seem to figure out how to call a variable from within an expression (it pastes the variable name).

Here is my code.

R2Val <- signif(summary(sMod_pre90)$r.squared[1], 2)
text(92, 4, expression(paste(R^2, " = ", R2Val)), adj = 0, cex = 0.85)

Answer 1

Use bquote(). Here is an example with dummy data:

set.seed(1)
DF <- data.frame(A = rnorm(100), B = rnorm(100))
mod <- lm(B ~ A, data = DF)
R2Val<-signif(summary(mod)$r.squared[1], 2)

The parts of the expression wrapped in .() get evaluated in the environment, i.e. the value of R2Val is substituted.

plot(B ~ A, data = DF)
text(1.5, 2, labels = bquote(R^2 == .(R2Val)), adj = 0, cex = 0.85)

Another potential solution is substitute, which works similarly:

plot(B ~ A, data = DF)
text(1.5, 2, labels = substitute(R^2 == A, list(A = R2Val)), adj = 0, cex = 0.85)