[R] simple interactions

Therneau, Terry M., Ph.D. therneau at mayo.edu
Fri Apr 15 13:58:22 CEST 2016

I'd like to get interaction terms in a model to be in another form.  Namely, suppose I had 
variables age and group, the latter a factor with levels A, B, C, with  age * group in the 
model.  What I would like are the variables "age:group=A", "age:group=B" and 
"age:group=C"  (and group itself of course).  The coefficients of the model will then be 
the age effect in group A, the age effect in group B and the age effect in C rather than 
the standard ones of an overall age effect followed by contrasts.  These is often a better 
format for tables in a publication.

Yes, I can reconstruct these from the original fit, but I have a lot of variables for 
several models and it would be easier to have an automatic form.  I suspect that there is 
an easy answer, but I don't see it.

Terry Therneau

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