How can I plot my R Squared value on my scatterplot using R?

Question

This seems a simple question, so I hope its a simple answer. I am plotting my points and fitting a linear model, which I can do OK. I then want to plot some summary statistics, for example the R Squared value, on the plot also. I can only seem to get the R Squared value at the command line. Any advice; do I need to be looking at ggplot or anything else? Thanks in advance.

#Does the plot
plot(df$VAR1, df$VAR2)
#Adds the line
abline(lm(df$VAR2~df$VAR1), col="red")
#Shows stats on command line
summary(lm(df$VAR2~df$VAR1))

Answer 1

You can abuse legend() because it has the handy logical placement:

R> DF <- data.frame(VAR1=rnorm(100), VAR2=rnorm(100))
R> with(DF, plot(VAR1, VAR2))
R> abline(fit <- lm(VAR2 ~ VAR1, data=DF), col='red')
R> legend("topright", bty="n", legend=paste("R2 is", 
+         format(summary(fit)$adj.r.squared, digits=4)))

Here bty="n" suppresses the box, and you need format() to shorten the display. Other text() is good, as are arguments main= and sub= to plot().

Answer 2

The text function places text into the current plot, it is one option for adding the r-squared value to a plot. Also look at the grconvertX and grconvertY functions for ways to find the location to place the text.

The corner.label and emptyspace functions in the plotrix package may also help.