What is the most elegant way to split data and produce seasonal boxplots?

Question

I want to produce seasonal boxplots for a lot of different time series. I hope that the code below clearly illustrates what I want to do.

My question is now, how to

Answer 1

To set months as ordered factor in any locale settings use a trick which can be found in help page for ?month.abb:

Sys.setlocale("LC_TIME", "German_Germany")
DF$month <- factor(format(DF$Time, "%b"), levels=format(ISOdate(2000, 1:12, 1), "%b"))

And you could plot it in lattice as well:

require(lattice)
bwplot(Data~month, DF, pch="|") # set pch to nice line instead of point