help with weights in lm and glm

      Dear all

      Could someone explain to why weights does not works in lm and glm
in the example below?
      Thanks in advance, Roseli.


       function(model){

        www<-fitted(model)
        lm(formula(model),weights=www)

       }

       The message error is: Error in eval(expr,envir,enclos): object
"www" not found.

Because it's looking in the environment of the model formula.

That's why it can find the other variables in the model even though you
didn't specify a dataframe to search.

You can use

function(model){
  www<-fitted(model)
  update(model, weights=www)
}

which does work (although it arguably shouldn't).

The handling of weights= in these modelling functions is a horrible wart
on the language.  Although they look like ordinary arguments they have
very strange scoping rules.


	-thomas