# R-alpha: model.matrix(.) does not allow `contrasts' ..

**Martin Maechler
**
Martin Maechler <maechler@stat.math.ethz.ch>

*Thu, 4 Dec 1997 18:23:23 +0100*

and this breaks multinom from the nnet library
[yes, Kurt, I'm working on that and I'll send you patches..]
Is this a bug or an (half-)intentional difference to S ?
---------------------
In R (0.50-0.60)
model.matrix(formula =, data =)
Arguments:
formula: A model formula or terms object
data: A data frame created with `model.frame'
In S-plus
USAGE:
model.matrix(object, ...)
model.matrix.default(terms.object, data, contrasts)
ARGUMENTS:
.....
contrasts: an optional list giving contrasts for some or all
of the factors appearing in the terms object. The
elements of the list should have the same name as the
variable and should be either a contrast matrix
(specifically, any full-rank matrix with as many rows as
there are levels in the factor), or else a function to
compute such a matrix given the number of levels. The
complete contrast list (anything given as an argument plus
any additional contrast matrices computed) will be
returned as the "contrasts" attribute of the model matrix,
and hence as the "contrasts" component of fitted models
returned by lm() and its descendants.
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