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: [email protected] [mailto:[email protected]] > On >> Behalf Of Gabor Grothendieck >> Sent: January-04-11 6:56 PM >> To: John Fox >> Cc: Sanford Weisberg; [email protected] >> Subject: Re: [Rd] scoping/non-standard evaluation issue >> >> On Tue, Jan 4, 2011 at 4:35 PM, John Fox <[email protected]> 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 >> >> ______________________________________________ >> [email protected] 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: [email protected] Priv: [email protected] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
