Print correlation data in same plot position across facets

Question

I have a faceted ggplot2 scatterplot, and would like to print summary statistics about the linear regression on each facet, as has been done here and here. Unlike those examples, I am using scales="free", and the ranges of the data in each facet are quite different, but I would like the summary statistics to show up in the same relative position in each facet (e.g. top right corner, or whatever). How can I specify to geom_text or annotate that the label should appear in the same position relative to the panel?

Where I am right now:

# Fake data
set.seed(2112)
x <- c(1:10, 6:15)
y <- x + c(runif(10), runif(10)*10)
l <- gl(2, 10)
d <- data.frame(x=x, y=y, l=l)

# Calculate a summary statistic (here, the r-squared) in a separate data frame
r_df <- ddply(d, .(l), summarise, rsq=round(summary(lm(y~x))$r.squared, 2))

# Use geom_text and a separate data frame to print the summary statistic
ggplot(d, aes(x=x, y=y)) +
  geom_text(data=r_df, aes(x=8, y=8, label=paste("rsq=", rsq)))+
  geom_point() + 
  facet_wrap(~l, scales="free")

I would like, instead, to have ggplot automatically position the text in the same relative position in each facet.

Answer 1

If you want to place them relative to the corners, you can achieve that by specifying an x or y position of Inf or -Inf:

ggplot(d, aes(x=x, y=y)) +
  geom_text(data=r_df, aes(label=paste("rsq=", rsq)), 
            x=-Inf, y=Inf, hjust=-0.2, vjust=1.2)+
  geom_point() + 
  facet_wrap(~l, scales="free")

I also adjusted hjust and vjust so the label was not in the exact corner of the graph by pushed away from it a bit.