[R] alternative to 'groups' for lattice bwplot()

[Sebastian Luque]

Hi,

Is there some alternative to the 'groups' argument in lattice's bwplot
function for boxplots? Say in the example below:

bwplot(yield ~ site | year, data = barley)

you want to have two side by side boxplots per site, corresponding to each
year in the barley data frame. Ideally, the space between boxplots of the
same site should be smaller than that between boxplots of different sites.

This seemed like a job for the 'groups' argument, but panel.bwplot doesn't
take it. I saw that boxplot() might do this for the particular example
above, but not for a more complex one with additional conditioning
variables (as in my actual problem).

I thought I'd find something about this in the archives, but I'm either
not using the right keywords or the question hasn't come up yet.

Some help on how to deal with this please?

-- 
Sebastian P. Luque