[R] Controlling text and strip arrangement in xyplot

[Juan Pablo Lewinger]

I've searched the archives and read the xyplot help but can't figure 
out the 2 lattice questions below?

Consider:

library(lattice)
DF <- data.frame(x=rnorm(20), y=rnorm(20), g1=rep(letters[1:2], 10),
                  g2=rep(LETTERS[1:2], each=10), 
g3=rep(rep(letters[3:4],each=5),2))

xyplot(y ~ x | g1 + g2, groups=g3, data=DF)

1) Is there a way to get one strip per row and column of panels as 
below instead of the default?


        _|__a__|__b__|
         |
       B
         |
        --
         |
       A
         |

2) How do I control the text of the strips so that for instance 
instead of "a" and "b" it reads"g1=alpha", "g1=beta" where "alpha" 
and "beta" stand for the corresponding greek symbols? (my difficulty 
here is not with the plotmath symbols but with controlling the text 
of the strips directly from the call to xyplot and not by renaming 
the levels of g1)

I'd appreciate any help!


Juan Pablo Lewinger
Department of Preventive Medicine
Keck School of Medicine
University of Southern California