Just in case someone else stumbles onto this thread and is facing a
similar issue: ?The quick solution for me turned out to be using Glm
and Predict in the rms package. Thanks go to Joshua and Ista for
helping me out with this issue. Double thanks go to Joshua for
suggesting I take a closer look at the rms package.
library(rms)
dat <- data.frame(xxA = rnorm(20,10), xxB = rnorm(20,20))
dat$out <- with(dat,xxA+xxB+xxA*xxB+rnorm(20,20))
rms.res <- Glm(out ~ scale(xxA)*scale(xxB),data=dat)
newdata <- as.data.frame(Predict(rms.res,xxA=c(-1,0,1),xxB=c(-1,0,1))[,1:3])
-----------------------------------
Russell S. Pierce, M.A.
Visual Cognition Lab
Department of Psychology
University of California, Riverside
900 University Avenue
Riverside, CA 92521
Lab Phone: (951) 827-7399