[R-sig-ME] How to extract num. of observations and groups used in a mixed model using gee package

[david oseguera montiel]

Does anyone know how can extract the number of observations and groups used
in a mixed model with gee package?
The summary function in gee package does not provide this information.
e.g.
data(warpbreaks)
summary(gee(breaks ~ tension, id=wool, data=warpbreaks,
corstr="exchangeable"))

I much appreciate any help,

David Oseguera Montiel
Phd student Wageningen University

pd. I asked this a few days ago in R-help list and I did not get any answer yet.