search for: panfak

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 eac...