I've added a time-transform ability to coxph: here is an example
fit <- coxph(Surv(time, status) ~ age + tt(age) + sex, data=lung,
tt=function(x, t, ...) x*log(t) )
The only role for tt() in the formula is to be noticed as a specials by
terms(). I currently have tt defined as a function
tt <- function(x)
It has to be exported in the namespace, documented, etc.
Is there a way to make tt() local to coxph, but still be found by
model.frame, so that it does not have to be global? It would seem to
be neater to do a marker transform like s() in gam, cluster() in coxph,
etc in this way, where the meaning is local to the enclosing function.
Terry Therneau
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