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).