情节传说中的R平方和n

Question

I would like a plot legend to contain both the R-squared value, as well as another value (the number of datapoints, n , in this case, but it's not specifically important). I'd like R-squared in the format R ^2 =, where R is italicised, and 2 is superscript.

Adding R-squared in this way on its own can be achieved on the following example using bquote

DF <- data.frame(VAR1=rnorm(100), VAR2=rnorm(100))
with(DF, plot(VAR1, VAR2))
fit <- lm(VAR2 ~ VAR1, data=DF)
r2 <- summary(fit)$adj.r.squared
mylabel = bquote(italic(R)^2 == .(format(r2, digits = 2)))
legend("bottomright", legend = mylabel ) # display legend

Adding both the R-squared value and n can be achieved in the following way (with credit to @DirkEddelbuettel here How can I plot my R Squared value on my scatterplot using R? )

legend("topleft", legend = c( paste("R2 =", format(r2, digits = 2)),
                              paste("n = ", nrow(DF)) ) )

However, I'm unable to find a way of modifying this to format the R ^2 in a way that doesn't also paste the call. For example,

legend("topleft", legend = c( expression(paste(italic(R)^2, " = ", format(r2, digits = 2))),
                          paste("n = ", nrow(DF)) ) )

will successfuly format the R ^2 but also pastes format(r2, digits = 2)

This seems as though it should be straightforward but I'm having no joy. Any help would be much appreciated, thanks.

Answer 1

Here is a way to do it, using atop to split within several lines.

# your code
DF <- data.frame(VAR1=rnorm(100), VAR2=rnorm(100))
with(DF, plot(VAR1, VAR2))
fit <- lm(VAR2 ~ VAR1, data=DF)
r2 <- summary(fit)$adj.r.squared
mylabel = bquote(italic(R)^2 == .(format(r2, digits = 2)))

# the legend
legend("topright", legend=bquote(atop(italic(R)^2 == .(format(r2, digits = 2)),"n" == .(nrow(DF)))),bty="n")

Note that I had to remove the box around the legend ( bty=n" ) as it is not well managed. For another solution involving mtext you may be interested in those two other post on stack and all links there:

Expression and new line in plot labels

Line break in expression()?