Dear all,
A small correction: I had a stray line in my f2(),
env <- new.env(parent=.GlobalEnv)
left over from yet another attempt; it can simply be removed.
Sorry for the confusion,
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 John Fox
> Sent: January-04-11 4:36 PM
> To: r-devel@r-project.org
> Cc: 'Sanford Weisberg'
> Subject: [Rd] scoping/non-standard evaluation issue
>
> 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?
>
> Thanks,
> John
>
> --------------------------------
> John Fox
> Senator William McMaster
> Professor of Social Statistics
> Department of Sociology
> McMaster University
> Hamilton, Ontario, Canada
> web: socserv.mcmaster.ca/jfox
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
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