[R] lattice: adding information on number of observations

[RINNER Heinrich]

Dear R-users,

I am using R version 2.9.1 and lattice 0.17-26 under windows.
In a lattice boxplot, I would like to add information on how many observations each singel boxplot is based upon.

For example (the basic plot):
# Begin R-code
library(lattice)
dat <- data.frame(panvar = rep(c("A","B","A","B"), c(3,7,4,6)), grp = rep(c("grp1", "grp2"), c(10,10)), val = rnorm(20))
dat
bwplot(val ~ grp | panvar, data = dat)
# End R-code

As in my real life data the number of observations in each subgroup will be quite different, I would like to include the number of observations each boxplot is based upon.
Aggregation will tell me the numbers:
# Begin R-code
aggregate(dat$val, by = list(dat$panvar, dat$grp), FUN = length)
# End R-code
But how to match these numbers with the plot (so that for example "n=3" will be written as text beneath panel A/group1)?

Any advice would be appreciated;
kind regards
Heinrich.