Dear Peter, You hit the nail on the head: I didn't (and don't) understand why mod.1 works -- which I attributed to my imperfect understanding of non-standard evaluation. Even if there's a bug allowing mod.1 to work, I wonder about the consequences of fixing it. That might break a lot of code. It would seem desirable, though, for mod.1 and mod.2 to behave the same.
Best, John > -----Original Message----- > From: peter dalgaard [mailto:pda...@gmail.com] > Sent: January-05-11 10:51 AM > To: John Fox > Cc: 'Gabor Grothendieck'; 'Sanford Weisberg'; r-devel@r-project.org > Subject: Re: [Rd] scoping/non-standard evaluation issue > > > On Jan 5, 2011, at 14:44 , John Fox wrote: > > > Dear Gabor, > > > > I used str() to look at the two objects but missed the difference that you > > found. What I didn't quite understand was why one model worked but not the > > other when both were defined at the command prompt in the global > > environment. > > I kind of suspect that the bug is that mod.1 works... I.e., I can vaguely > make out the contours of why mod.2 is not supposed to work and if that is > true, neither should mod.1. However, if so, something clearly needs more > work. Possibly, some of the people who worked on implement formula > environments may want to chime in? (It's been a while, though.) > > > > > Thanks, > > 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 Gabor Grothendieck > >> Sent: January-04-11 6:56 PM > >> To: John Fox > >> Cc: Sanford Weisberg; r-devel@r-project.org > >> Subject: Re: [Rd] scoping/non-standard evaluation issue > >> > >> On Tue, Jan 4, 2011 at 4:35 PM, John Fox <j...@mcmaster.ca> 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 there is something wrong with R here since the formula in the > >> call component of mod.1 has a "call" class whereas the corresponding > >> call component of mod.2 has "formula" class: > >> > >>> class(mod.1$call[[2]]) > >> [1] "call" > >>> class(mod.2$call[[2]]) > >> [1] "formula" > >> > >> If we reset call[[2]] to have "call" class then it works: > >> > >>> mod.2a <- mod.2 > >>> mod.2a$call[[2]] <- as.call(as.list(mod.2a$call[[2]])) > >>> f(mod.2a) > >> > >> Call: > >> lm(formula = Employed ~ GNP.deflator + GNP + Unemployed + Armed.Forces + > >> Population + Year, data = longley, subset = subs) > >> > >> Coefficients: > >> (Intercept) GNP.deflator GNP Unemployed Armed.Forces > >> Population Year > >> 3.641e+03 8.394e-03 6.909e-02 -3.971e-03 -8.595e-03 > >> 1.164e+00 -1.911e+00 > >> > >> > >> -- > >> Statistics & Software Consulting > >> GKX Group, GKX Associates Inc. > >> tel: 1-877-GKX-GROUP > >> email: ggrothendieck at gmail.com > >> > >> ______________________________________________ > >> R-devel@r-project.org mailing list > >> https://stat.ethz.ch/mailman/listinfo/r-devel > > > > -- > 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
