formula<-Surv(time,status)~factor(edtrt)
tt<-terms(formula)
mf<-model.frame(tt,data=pbc)
mm<-model.matrix(tt,mf)
## a few rows of data
mm[1:3,]
## old-style assign attribute
attr(mm,"assign")
## new-style assign attribute
attrassign(mm,tt)
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