Dear Peter, I played around a bit with your suggestion but wasn't able to get it to work.
Thanks for this. John -------------------------------- John Fox Senator William McMaster Professor of Social Statistics Department of Sociology McMaster University Hamilton, Ontario, Canada web: socserv.mcmaster.ca/jfox > -----Original Message----- > From: r-devel-boun...@r-project.org [mailto:r-devel-boun...@r-project.org] On > Behalf Of peter dalgaard > Sent: January-04-11 6:05 PM > To: John Fox > Cc: 'Sanford Weisberg'; r-devel@r-project.org > Subject: Re: [Rd] scoping/non-standard evaluation issue > > > On Jan 4, 2011, at 22:35 , John Fox wrote: > > > Dear r-devel list members, > > > > On a couple of occasions I've encountered the issue illustrated by the > > following examples: > > > > --------- snip ----------- > > > >> mod.1 <- lm(Employed ~ GNP.deflator + GNP + Unemployed + > > + Armed.Forces + Population + Year, data=longley) > > > >> mod.2 <- update(mod.1, . ~ . - Year + Year) > > > >> all.equal(mod.1, mod.2) > > [1] TRUE > >> > >> f <- function(mod){ > > + subs <- 1:10 > > + update(mod, subset=subs) > > + } > > > >> f(mod.1) > > > > Call: > > lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > > Population + Year, data = longley, subset = subs) > > > > Coefficients: > > (Intercept) GNP.deflator GNP Unemployed Armed.Forces > > 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > > Population Year > > 1.164e+00 -1.911e+00 > > > >> f(mod.2) > > Error in eval(expr, envir, enclos) : object 'subs' not found > > > > --------- snip ----------- > > > > I *almost* understand what's going -- that is, clearly mod.1 and mod.2, or > > the formulas therein, are associated with different environments, but I > > don't quite see why. > > > > Anyway, here are two "solutions" that work, but neither is in my view > > desirable: > > > > --------- snip ----------- > > > >> f1 <- function(mod){ > > + assign(".subs", 1:10, envir=.GlobalEnv) > > + on.exit(remove(".subs", envir=.GlobalEnv)) > > + update(mod, subset=.subs) > > + } > > > >> f1(mod.1) > > > > Call: > > lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > > Population + Year, data = longley, subset = .subs) > > > > Coefficients: > > (Intercept) GNP.deflator GNP Unemployed Armed.Forces > > 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > > Population Year > > 1.164e+00 -1.911e+00 > > > >> f1(mod.2) > > > > Call: > > lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > > Population + Year, data = longley, subset = .subs) > > > > Coefficients: > > (Intercept) GNP.deflator GNP Unemployed Armed.Forces > > 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > > Population Year > > 1.164e+00 -1.911e+00 > > > >> f2 <- function(mod){ > > + env <- new.env(parent=.GlobalEnv) > > + attach(NULL) > > + on.exit(detach()) > > + assign(".subs", 1:10, pos=2) > > + update(mod, subset=.subs) > > + } > > > >> f2(mod.1) > > > > Call: > > lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > > Population + Year, data = longley, subset = .subs) > > > > Coefficients: > > (Intercept) GNP.deflator GNP Unemployed Armed.Forces > > 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > > Population Year > > 1.164e+00 -1.911e+00 > > > >> f2(mod.2) > > > > Call: > > lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > > Population + Year, data = longley, subset = .subs) > > > > Coefficients: > > (Intercept) GNP.deflator GNP Unemployed Armed.Forces > > 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > > Population Year > > 1.164e+00 -1.911e+00 > > > > --------- snip ----------- > > > > The problem with f1() is that it will clobber a variable named .subs in the > > global environment; the problem with f2() is that .subs can be masked by a > > variable in the global environment. > > > > Is there a better approach? > > I think the best way would be to modify the environment of the formula. > Something like the below, except that it doesn't actually work... > > f3 <- function(mod) { > f <- formula(mod) > environment(f) <- e <- new.env(parent=environment(f)) > mod <- update(mod, formula=f) > evalq(.subs <- 1:10, e) > update(mod, subset=.subs) > } > > The catch is that it is not quite so easy to update the formula of a model. > > -- > Peter Dalgaard > Center for Statistics, Copenhagen Business School > Solbjerg Plads 3, 2000 Frederiksberg, Denmark > Phone: (+45)38153501 > Email: pd....@cbs.dk Priv: pda...@gmail.com > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
