[Rd] new behavior of model.response

[Therneau, Terry M., Ph.D.]

Charles Berry pointed out an error in my reasoning.   In the current survival I forgot the 
S3method line for length in the NAMESPACE file, so the behavior is really not new.  
Nonetheless it remains surprising and non-intuitive.  Why does model.response sometimes 
attach spurious names, when the Surv object itself does not have them?

Terry


tmt% R --vanilla
R version 3.4.2 (2017-09-28) -- "Short Summer"

test <- data.frame(time=1:8, status=rep(0:1, 4), age=60:67)
row.names(test) <- letters[1:8]

library(survival)

mf2 <- model.frame(Surv(time, status) ~ age, data=test)
names(mf2[[1]])
# NULL
names(model.response(mf2))
# NULL

length.Surv <- survival:::length.Surv

names(model.response(mf2))
  # [1] "a" "b" "c" "d" "e" "f" "g" "h" NA  NA  NA  NA  NA  NA  NA NA


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