From Torsten.Hothorn at rzmail.uni-erlangen.de  Thu May  8 10:17:50 2003
From: Torsten.Hothorn at rzmail.uni-erlangen.de (Torsten Hothorn)
Date: Thu May  8 09:18:01 2003
Subject: [Rd] contrasts
In-Reply-To: <Pine.LNX.4.44.0305071609340.5546-100000@gannet.stats>
References: <Pine.LNX.4.44.0305071609340.5546-100000@gannet.stats>
Message-ID: <Pine.LNX.4.51.0305080913080.16342@artemis.imbe.med.uni-erlangen.de>


> On Wed, 7 May 2003, Torsten Hothorn wrote:
>
> > I spent some time now trying to understand how functions for the
> > computation of contrasts
> >
> > contr.foo(n, contrasts=TRUE)
> >
> > passed to model.matrix are called. My problem is
> > that for the computation of some contrasts one needs `n' to be the number
> > of observations at each level of the factor of interest and for others the
> > number of levels is sufficient. For example, `contr.treatment' has code
> > for handling vector valued `n' (and ?contrasts states that `n' may be a vector).
> >
> > Where can I find the condition under which `n = nlevel(x)' or `n =
> > table(x)' or how can I define what I would like to see?
>
> >From model.matrix, only the number of levels is passed: src/main/model.c
> line 1626 (in R-devel and probably also 1.7.0).

Thank you! Therefore one cannot compute contrasts that depend on
the number of observations at each level, right? Looking at the code in
`contr.treatment' that handles this case: may I conclude that this is on
the wishlist?

Torsten

>
> --
> Brian D. Ripley,                  ripley@stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>
>


[Rd] contrasts
Torsten Hothorn