Hi Peter, > --------- Forwarded message ---------- > From: Peter Schmidtke <pschmid...@mmb.pcb.ub.es> > To: r-help@r-project.org > Date: Wed, 15 Jul 2009 12:27:17 +0200 > Subject: [R] interacting variables in a formulae in R > Dear R Mailing Subscribers, > > I just have a question of how R handles interacting variables in model > creation using glm for instance. > > if I write : > > >> > model=glm(solution~descriptor1+descriptor2+descriptor3,family=binomial(link="logit")) > > I should end up with coefficients for a logistic model that I can introduce > easily in the mathematical form of such a model (weighted sum of these > descriptors). > > But how do I have to interpret what R does with interacting terms, like > this? : > > >> > model=glm(solution~descriptor1:descriptor2+descriptor3,family=binomial(link="logit")) > > What does R with the numerical values of descriptor1 and 2 in order to fit > the data? How I can rewrite the model in a mathematical form? >
Take a look at ?contrasts and ?model.matrix At least I think that's what you're after... -Ista > Thanks in advance. > > Best regards. > -- > > Peter Schmidtke > > ---------------------- > PhD Student at the Molecular Modeling and Bioinformatics Group > Dep. Physical Chemistry > Faculty of Pharmacy > University of Barcelona ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.