From the NEWS for 2.13.0-to-be
\item \code{drop.terms} and the \code{[} method for class
\code{"terms"} no longer add back an intercept. (Reported by
Niels Hansen.)
so it has been fixed, just not rolled out yet.
On Mon, 21 Feb 2011, Terry Therneau wrote:
This arose when working on an addition to coxph, which has the features
that the X matrix never has an intercept column, and we remove strata()
terms before computing an X matrix. The surprise: when a terms object
is subset the intercept attribute is turned back on.
My lines 2 and 3 below were being executed just before a call to
model.frame. The simple solution was of course to do them in the
opposite order so I am not waiting on a "fix".
Not to mention that I am not sure a fix is required, though I was
surprised.
Terry T.
tmt1131% R
R version 2.12.0 (2010-10-15)
Copyright (C) 2010 The R Foundation for Statistical Computing
ISBN 3-900051-07-0
Platform: x86_64-unknown-linux-gnu (64-bit)
test <- terms(Surv(time, status) ~ age + strata(ph.ecog),
+ specials='strata')
attr(test, 'intercept') <- 0 #turn off intercept
test <- test[-2] #remove strata
test
Surv(time, status) ~ age
attr(,"variables")
list(Surv(time, status), age)
attr(,"factors")
age
Surv(time, status) 0
age 1
attr(,"term.labels")
[1] "age"
attr(,"specials")
attr(,"specials")$strata
NULL
attr(,"order")
[1] 1
attr(,"intercept")
[1] 1
attr(,"response")
[1] 1
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Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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