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Hi all, I suppose this is a very simple question, but as I've lost already a bit of time with it, without being able to get what I wanted, I'm addressing the question to the group in the hope someone can help me. I pretend to plot the richness of herbaceous species (RichHN) as a function of time since remnant isolation (Isol) conditioned to the area of the remnant (fArea - this is a factor with 3 classes). I also want to differentiate the sites plotted using a grouping binary variable (Urb). So far, I've written this: extinction<-xyplot(RichHN~Isol|fArea, da...