Example of annotating each ggplot2 facet with the number of points it displays

facet_annotation.r

# Strings ain't factors
options(stringsAsFactors = FALSE)



library(ggplot2)
library(plyr)

# How many in each group?
cyl_count <- count(mtcars, "cyl")

# Make it a little prettier...
cyl_count$freq <- paste("N =", cyl_count$freq)


# Plot two layers with their own datasets
# Arbitrary x and y for the text positioning, although you get get algorithmic with it
# Na-na na na na na-na
ggplot() +
    geom_point(data = mtcars, aes(x = disp, y = hp)) +
    geom_text(data = cyl_count, aes(x = 400, y = 300, label = freq)) +
    facet_wrap( ~ cyl)