R help - Jan 2002 - taking variables from data.frame

Dear all,
Two of the arguments of my function fn(), say, are a glm-obj and a variable
in the data.frame where there are the variable of the obj too.
Is there a way to build a function that takes the variables form the same
data.frame? For instance, the update() function does so:
>obj<-glm(....,data=mydata)
>update(obj,.~.+x) #works becuse it searches x in mydata
But for my function:
>fn(....,obj, mydata$x) #it works
and
>fn(....,obj, x) #doesn't works: x not found!
Of course I can attach the data.frame in the function by something like:

fn<-function(....,data){
 attach(data)
 ....
 detach()
 }

but is there anyone that can suggest me anything better?
Thank you very much for your help,
vito
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On Fri, 4 Jan 2002, MUGGEO VITO wrote:
> Two of the arguments of my function fn(), say, are a glm-obj and a variable
> in the data.frame where there are the variable of the obj too.
> Is there a way to build a function that takes the variables form the same
> data.frame? For instance, the update() function does so:
No, model.frame called from the glm function does so, not update.  update
just creates a new call to glm, and calls it.
> >obj<-glm(....,data=mydata)
> >update(obj,.~.+x) #works becuse it searches x in mydata
>
> But for my function:
> >fn(....,obj, mydata$x) #it works
>
> and
> >fn(....,obj, x) #doesn't works: x not found!
>
> Of course I can attach the data.frame in the function by something like:
>
> fn<-function(....,data){
>  attach(data)
>  ....
>  detach()
>  }
>
> but is there anyone that can suggest me anything better?
Hint: try ?eval.  The critical line in model.frame.default is

    variables <- eval(attr(formula, "variables"), data, env)


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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