Grouped bwplots?

Dear list,

I am sorry for asking you this, but I am trying to do again what I
thought I have done before, although this time it does not work.

So, given the data set:

testdf <- data.frame(grfak=sample(c("One","Two"),size=100,replace=TRUE),
panfak= sample(c("Yes","No"),size=100,replace=TRUE), xfak=
sample(c("Yep","Nope"),size=100,replace=TRUE),  d=rnorm(100))

I would like to do:

bwplot(d ~ xfak | panfak,data=testdf, groups= grfak)

where the groups argument makes a difference (as in dividing each box
into two by group).
Is this possible to do?

Dear list,

I am sorry for asking you this, but I am trying to do again what I
thought I have done before, although this time it does not work.

So, given the data set:

testdf <- data.frame(grfak=sample(c("One","Two"),size=100,replace=TRUE), panfak= sample(c("Yes","No"),size=100,replace=TRUE), xfak= sample(c("Yep","Nope"),size=100,replace=TRUE),  d=rnorm(100))

I would like to do:

bwplot(d ~ xfak | panfak,data=testdf, groups= grfak)

where the groups argument makes a difference (as in dividing each box
into two by group).
Is this possible to do? If so, what I am doing wrong?