Thanks to you for your responses. Professor Brian Ripley provided an
answer. He actually described the situation where I experienced the
problem, which is slightly more complicated than what I said in the
message. Suppose I have a function
myfun <- function(data) {
survfit(coxph(Surv(time, cens) ~ group, data=data)
}
Then
> myfun(mydata)
doesn't work. Modify the function as suggested by Brian
myfun <- function(data) {
dd <- deparse(substitute(data))
call <- paste("survfit(coxph(Surv(time, cens) ~ group, data=", dd, "))")
eval(parse(text=call), sys.parent())
}
then it works. However, if I have another function calling it
myanother <- function(data) {
myfun(data)
}
then
> myanother(mydata)
won't work again. So in this case, a "better" way seems to be the
first method suggested in Brian's message: assign the mydata to frame 1.
Although it solves my problem, it has an undesirable side-effect:
mydata is now visible to all nested functions in the call.
I understand that all of these problems come from eval(Call) in
model.frame.coxph. Apparently adding sys.parent() to eval(Call) will
not solve the problem. I wonder whether there is a neat fix to
model.frame.coxph (or other similar functions) so that I don't
need to worry about the frames in such a straightforward function
call.
BTW, Patrick Burns's S Poetry is very helpful resource. I did search
it for a quick solution when I got this problem, but I went to a wrong
place.
Regards,
Paul.
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