On Wed, 13 Aug 2008, Pete Berlin wrote:
Hi all,
I'm having some difficulty passing arguments into lm() from within a
function, and I was hoping someone wiser in the ways of R could tell me
what I'm doing wrong. I have the following:
lmwrap <- function(...) {
wts <- somefunction()
print(wts) # This works, wts has the values I expect
fit <- lm(weights=wts,...)
return(fit)
}
If I call my function lmwrap, I get the the following error:
lmwrap(a~b)
Error in eval(expr, envir, enclos) : object "wts" not found
Correct. The help (?lm) says
All of 'weights', 'subset' and 'offset' are evaluated in the same
way as variables in 'formula', that is first in 'data' and then in
the environment of 'formula'.
A traceback gives me the following:
8: eval(expr, envir, enclos)
7: eval(extras, data, env)
6: model.frame.default(formula = ..1, weights = wts, drop.unused.levels =
TRUE)
5: model.frame(formula = ..1, weights = wts, drop.unused.levels = TRUE)
4: eval(expr, envir, enclos)
3: eval(mf, parent.frame())
2: lm(weights = wts, ...)
1: wraplm(a ~ b)
It seems like whatever environment lm is trying to eval wts in doesn't
have it defined.
Could anyone tell me what I'm doing wrong?
As a sidenote, I do have a workaround, but this strikes me as really the
wrong thing to do. I replace the call to lm with:
eval(substitute(lm(weights = dummy,...),list(dummy=wts)))
which works.
It's one workaround, but working with the scoping rules is better. Hint:
use the 'data' argument to lm.
--
Brian D. Ripley, [EMAIL PROTECTED]
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 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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