[R] specifying models ":" and %in% and soforth

[Daniel Lakeland]

If a and b are factor variables are there any differences between 

~ a:b
~ b:a 
~ a %in% b
~ b %in% a

playing with model.matrix doesn't show any differences in the
resultant matrices, which is what I expect based on my understanding
if what's being specified.

I'm hoping that someone can clarify what (if any) the differences are.

Thanks,
Dan

-- 
Daniel Lakeland
dlakelan at street-artists.org
http://www.street-artists.org/~dlakelan