[R] deviance in glm

[Chong Gu]

Folks,

I am not sure if it's a feature or a "bug".  The same is observed in
Splus.

Suppose I have Poisson counts, and I would like to estimate the
parameter using glm.  I would assume I can feed it the individual
counts, or I can feed it the distinctive counts with the frequency as
the weights, and I would get the same results.  I do, but the deviance
df are returned differently.  Here is a short session.

y<-rpois(1000,5)
fr<-as.vector(table(y))
yy<-0:(length(fr)-1)
glm(y~1,poisson)
glm(yy~1,poisson,weight=fr)

I believe the first call to glm gives the correct df, but with real
data, do I have to break up the tabulated data to get it right from R
(or Splus), or I just have to manually calculate the df?  Can this be
potentially misleading to practitioners?

Or maybe my thinking was off?

I tried similar things with Bernoulli data and got similar results.

Chong Gu
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