lm() and interactions in model formula for x passed as matrix
Thanks for the replies. I was just thinking that, for a two variable example, doing X<-cbind(x1,x2,x1*x2) lm(y~X) would work. So maybe that's what I'll do. This also allows me to pick and choose which interactions to include. Cheers Bill On Sun, Dec 5, 2010 at 8:19 PM, William Simpson
<william.a.simpson at gmail.com> wrote:
Suppose I have x variables x1, x2, x3 (however in general I don't know how many x variables there are). I can do X<-cbind(x1,x2,x3) lm(y ~ X) This fits the no-interaction model with b0, b1, b2, b3. How can I get lm() to fit the model that includes interactions when I pass X to lm()? For my example, lm(y~x1*x2*x3) I am looking for something along the lines of lm(y~X ...) where ... is some extra stuff I need to fill in. Thanks for any help. Bill