Corner Labels in ggplot2

Question

I\'m interested in trying to create simple corner labels for a multipanel figure I am preparing in ggplot. This is similar to this previously asked question, but the answers

Answer 1

An example:

d <- data.frame(x = runif(16),
                y = runif(16),
                grp = rep(letters[1:4],each = 4))

ggplot(d,aes(x = x,y = y)) + 
facet_wrap(~grp) + 
geom_point() + 
theme(strip.text = element_text(hjust = -0.05),
      strip.background = element_blank())