Luke, A really useful thing to do would be to read section 11.1 of "An Introduction to R", which comes with your R installation.
Peter Ehlers Luke wrote: > Thanks, Christos. Another relevant question: > > If I want to include the interaction term consisting of V2 and V3 (they are > numeric vectors), should I use: > > y ~ 1 + V2:V3 or y ~ 1 + I(V2*V3) > > or both are good? > > -Luke > > On 4/17/06, Christos Hatzis <[EMAIL PROTECTED]> wrote: > >>If you want the quadratic term, you need to pass it as an argument in >>function I(): >> >>y ~ 1 + V1 + V3 + I(V3^2) >> >>This is documented in ?formula >> >>-Christos >> >>-----Original Message----- >>From: [EMAIL PROTECTED] >>[mailto:[EMAIL PROTECTED] On Behalf Of Luke >>Sent: Monday, April 17, 2006 12:08 AM >>To: R-help@stat.math.ethz.ch >>Subject: [R] interaction terms in formula of lm or glm >> >>I would like to include pairwise interaction terms for lm(). For example, >>I >>want to include the quadratic term of variable "V3". >> >> >>>my.formula >> >>y ~ 1 + V1 + V3 + V3:V3 >> >> >>>my.data >> >> y V1 V2 V3 >>1 31 1 42 140 >>2 32 0 43 120 >>3 33 0 57 150 >>4 34 0 55 132 >> >> >>>foo <- lm(my.formula, data = my.data) >> >>>foo$coefficients >> >>(Intercept) V1 V3 >>29.47368421 -2.15789474 0.02631579 >> >>Why do the foo coefficients not include V3:V3 ? >> >>I thought that the variable "V3:V3" has the values of squares of V3 >>elements, that is, >>V3:V3 >>140*140 >>120*120 >>.... >>Am I wrong? >> >>If I specify a fouth varaible "V4" with square values of V3, and the >>formula >>is y ~ 1 + V1 + V3 + V4, it seems that the foo will give me different in >>and >>out-sample predictions. >> >>-Luke >> >> [[alternative HTML version deleted]] >> >>______________________________________________ >>R-help@stat.math.ethz.ch mailing list >>https://stat.ethz.ch/mailman/listinfo/r-help >>PLEASE do read the posting guide! >>http://www.R-project.org/posting-guide.html >> >> >> > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html