I'm not sure if this will help, but it's worth a try. Do the regression as I suggested before, extract the model matrix and remove the "offending" column. I'm assuming you don't know in advance how many levels there are in the factor. Then use this to perform the regression. Something like this:
m1 <- lm(x ~ fd:y + fd) mm <- model.matrix(m1) nl <- length(levels(fd)) newdat <- mm[,-c(1,nl)] lm(x ~ newdat) On 30/11/06, Andreas Goesele <[EMAIL PROTECTED]> wrote: > "David Barron" <[EMAIL PROTECTED]> writes: > > > I'm not sure that's possible, given that you would effectively be > > fitting a different model to those cases with fd==1, wouldn't you? > > This was what I was afraid of. But your argument I don't understand > completely. > > Do you want to say, that the *model* x = a + b1*fd2 + b2*fd3 + > c1*fd2*y + c1*fd3*y doesn't make sense as fd2 together with fd3 > doesn't cover all cases? And that because the model doesn't make sense > it is not easily implemented in R? > > My problem is that I have to estimate a model of this kind whether it > makes sense or not. So I still would be happy to find an easy and > elegant way... > > > On 29/11/06, Andreas Goesele <[EMAIL PROTECTED]> wrote: > >> "David Barron" <[EMAIL PROTECTED]> writes: > >> > >> > Is this what you want? > >> > > >> > lm(y ~ fd + fd:y) > >> > >> Thanks for you fast reply. But it's not what I wanted. > >> > >> To make it clearer I have to correct the first part of what I wrote: > >> > >> > On 29/11/06, Andreas Goesele <[EMAIL PROTECTED]> wrote: > >> > >> >> I would like to estimate something like y = a + b*d2*y + c*d3*y > >> >> where the dummies are created from some vector d with three > >> >> (actually many more) levels using factor(). But either there is > >> >> included the variable y or d1*y. How could I get rid of these? > >> > >> This should have been something like: > >> > >> x = a + b1*d2 + b2*d3 + c1*d2*y + c1*d3*y > >> > >> When I change your suggestion to lm(x ~ fd + fd:y) I get the same as > >> for lm(x ~ fd*y - y), namely: > >> > >> Coefficients: > >> (Intercept) fd2 fd3 fd1:y fd2:y fd3:y > >> 2.4231 9.5769 6.1822 -0.1154 -1.0000 -0.4474 > >> > >> What I want is: > >> > >> Coefficients: > >> (Intercept) fd2 fd3 fd2:y fd3:y > >> > >> Thanks a lot again! > >> > >> Andreas Goesele > >> > >> -- > >> Andreas Gösele Omnis enim res, quae dando non deficit, > >> Inst. f. Gesellschaftspolitik dum habetur et non datur, > >> Kaulbachstr. 31a, 80539 München nondum habetur, quomodo habenda est. > >> E-mail: [EMAIL PROTECTED] (Augustinus) > >> > >> ______________________________________________ > >> R-help@stat.math.ethz.ch mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-help > >> PLEASE do read the posting guide > >> http://www.R-project.org/posting-guide.html > >> and provide commented, minimal, self-contained, reproducible code. > >> > > > > > > -- > > ================================= > > David Barron > > Said Business School > > University of Oxford > > Park End Street > > Oxford OX1 1HP > > > > > > -- > Andreas Gösele Omnis enim res, quae dando non deficit, > Inst. f. Gesellschaftspolitik dum habetur et non datur, > Kaulbachstr. 31a, 80539 München nondum habetur, quomodo habenda est. > E-mail: [EMAIL PROTECTED] (Augustinus) > -- ================================= David Barron Said Business School University of Oxford Park End Street Oxford OX1 1HP ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
