Torsten.Hothorn at rzmail.uni-erlangen.de
Thu May 8 10:17:50 MEST 2003
> 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
> Brian D. Ripley, ripley at 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
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