The help page for the survfit function says it expects a formula as its
first argument so try:
> sleepfit <- survfit(Surv(timeb, death)~1, data = sleep)
David
Sent from my iPhone ... so unable to test.
This was a recent (well, 2007) change in behaviour. Previously the function
did some tricks to make either approach work, which could be described as
'clever' or 'too clever by half'.
-thomas
Certainly the latter, a design mistake that I finally admitted and corrected. The
trouble is this usage
fit <- survfit(Surv(time, status), data=mine)
The data, subset, weights, and na.action arguments are all meant to work with formulas.
The first argument above isn't a formula. This left survfit with the quandry of how to
recognize that the first argument is a "Surv" object and not a formula, and do something
differently. Which leads to a stalemate
a. One doesn't know what type of object the first argument is until it
is evaluated
b. Evaluation will fail, however, unless it is evaluated in the
"data=mine" context
c. The function that does that process (model.frame) expects a formula
as its first arg
My program needed to know the answer to a) in order to transform the first arg into a
formula and correctly execute c), but needed the answer from c) to know if that was necessary.
The old code peeked back at the actual string that was typed by the user, looking for the
letters "Surv", but was easily fooled.
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