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2002 Oct 24
3
model.matrix (via predict) (PR#2206)
...from: (NULL) (168.140.227.9) The following code produces incorrect fitted values in version 1.5.1 and an error in 1.6.0 Error in "contrasts<-"(*tmp*, value = "contr.treatment") : contrasts apply only to factors In addition: Warning message: variable ihalf is not a factor in: model.frame.default(object, data, xlev = xlev) The problem in 1.5.1 seems to be model.matrix return inconsistently ordered interaction terms. There are abviously several work arounds. ### Start of example dfr <- expand.grid(i=0:154,j=0:154) dfr <- dfr[with(dfr,i+j<=...