R help - Oct 2002 - dropterm in a function

I'm trying to use 'dropterm' (from MASS) in a function along the
lines

run <- function(dat){
  fit <- (something)(Y ~ (something), data = dat)
  lr <- dropterm(fit, test = "Chisq")
  return(fit, lr)
}

but running 'run' I get (those scoping rules again...?)

Error in terms.formula(formula, special, data = data) :
        Object "dat" not found

This works fine at the command line. Can I send 'dat' to
'dropterm'
somehow, or what should I do?

Thankful for any suggestion, including reading certain books!

G?ran


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On Fri, 4 Oct 2002, [iso-8859-1] Göran Broström wrote:
>
> I'm trying to use 'dropterm' (from MASS) in a function along
the lines
>
> run <- function(dat){
>   fit <- (something)(Y ~ (something), data = dat)
>   lr <- dropterm(fit, test = "Chisq")
>   return(fit, lr)
> }
>
> but running 'run' I get (those scoping rules again...?)
>
> Error in terms.formula(formula, special, data = data) :
>         Object "dat" not found
>
> This works fine at the command line. Can I send 'dat' to
'dropterm'
> somehow, or what should I do?
>
What is "something"? If "something" is lm or glm this works
for me. I
would expect it not to work for lme().

This isn't precisely a scoping rules issue, but a nonstandard evaluation
rules one.  Functions using model formulas have to do strange things to
evaluate variables, and they don't always work consistently.

	-thomas


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