Could you explain how memory problems may arise? I understand that by using model=FALSE, we can reduce the memory required. But if we did not, what kinds of problems may arise. I have run into a possible memory leak that I have not been able to work around (using yags, not lm). I am trying to gain insight into this problem. Thanks, Juliet
On Sat, Feb 14, 2009 at 10:18 PM, <[email protected]> wrote: > Without arguing you case I would point out that the data need not be there in > l$model: > >> l <- lm(y ~ x, data=ex, model = FALSE) >> l > > Call: > lm(formula = y ~ x, data = ex, model = FALSE) > > Coefficients: > (Intercept) x > 0.1310 -0.1736 > >> l$model > NULL > > Model objects are often huge simply because by default they squirrel away a > copy of the original data inside themselves. One way to avoid memory > problems can be only to keep this backup copy within the fitted model object > only when you really need to do so, which is not all that often, in fact. > > I can see why step() (and allies) do not work the way you think they should. > These functions use the call component of the fitted model object and modify > that. And if the call component says your data are in the data frame 'ex', > they take you seriously. They your word for it. We're not dealing with > Microsoft software here, you know. > > Bill Venables > http://www.cmis.csiro.au/bill.venables/ > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Adam D. I. Kramer > Sent: Sunday, 15 February 2009 12:44 PM > To: [email protected] > Subject: [R] Issue with step(): Fails to look for object$model > > Hi, > > I'm playing around with stepwise regression, using the step > function, and believe I have found a bug (or at least, a strong case for > improvement): > >> ex <- data.frame(y=rnorm(100),x=rnorm(100)) >> l <- lm(y ~ x, data=ex) >> step(l) > [output is correct] >> rm(ex) >> step(l) > Start: AIC=11.79 > y ~ x > > Df Sum of Sq RSS AIC > - x 1 0.120 108.221 9.900 > <none> 108.100 11.789 > Error in inherits(x, "data.frame") : object "ex" not found > > ...ex is not found, so step fails. However, all of the necessary data to run > the step function is present in l$model. > > I would also argue that step() *should* use l$model if at all possible, as > it seems reasonable to expect that ex may undergo changes. Further, step() > does not appear to test any other columns present in ex (even if > direction="both" is specified), unless they are specified in scope. > > If I am misunderstanding step() or if there is a good reason why it operates > this way, please let me know! > > --Adam > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
