[R] updating glm

[vito muggeo]

Dear all,
my function fn() (see code below) just takes a glm object and updates it by
including a function of a specified variable in dataframe.

 x<-1:50
 y<-rnorm(50)
 d<-data.frame(yy=y,xx=x);rm(x,y)
 o<-glm(yy~xx,data=d)

> fn(obj=o,x=xx)

Call:  glm(formula = yy ~ xx + x1, data = obj$data)
....[SNIP]....

It works but I have two problems:
1)In the returning glm object the name of the dataframe is "obj$data", but I
would like to get the original one, i.e. "d";

2)fn() does not work if glm() is called without the data argument, namely
> attach(d)
>  o<-glm(yy~xx)
> fn(obj=o,x=xx)
Error in eval(expr, envir, enclos) : Object "x1" not found

Here there seems to be some problem with the scoping rule; could you suggest
me how solve this problem? Also I'm almost sure that there exist a much more
elegant solution instead of the mine used; I tried get(), environment() and
friends, but without any success....Could you suggest me anything?

thanks in advance,
vito


#########
function(obj,x){
 if(!is.null(obj$call$data)){
  attach(eval(obj$call$data))
  on.exit(detach(eval(obj$call$data)))
    }
 x1<-ifelse(x>mean(x),1,0)
 if(!is.null(obj$call$data)) obj$data$x1<-x1
 obj1<-update(obj,.~.+x1,data=obj$data)
 return(obj1)
 }