Easily add an '(all)' facet to facet_wrap in ggplot2?

Question

I have data that looks like this example in the facet_wrap documentation:

_{(source: ggplot2.org)}

I would like to fill the last facet with the overall view, using all data.

Is there an easy way to add a 'total' facet with facet_wrap? It's easy to add margins to facet_grid, but that option does not exist in facet_wrap.

Note: using facet_grid is not an option if you want a quadrant as in the plot above, which requires the ncol or nrow arguments from facet_wrap.

Answer 1

library(ggplot2)

p <- qplot(displ, hwy, data = transform(mpg, cyl = as.character(cyl)))
cyl6 <- subset(mpg, cyl == 6)
p + geom_point(data = transform(cyl6, cyl = "7"), colour = "red") +
  geom_point(data = transform(mpg, cyl = "all"), colour = "blue") +
  facet_wrap(~ cyl)