From ripley at stats.ox.ac.uk  Wed May  7 17:12:14 2003
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Wed May  7 17:12:50 2003
Subject: [Rd] contrasts
In-Reply-To: <Pine.LNX.4.51.0305071649330.28422@artemis.imbe.med.uni-erlangen.de>
Message-ID: <Pine.LNX.4.44.0305071609340.5546-100000@gannet.stats>

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).

-- 
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
Prof Brian Ripley