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John Fox

2011-Jan-04 21:35 UTC

[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

John Fox

2011-Jan-04 21:55 UTC

head link

[Rd] scoping/non-standard evaluation issue

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-bounces at r-project.org [mailto:r-devel-bounces at
r-project.org]
On> Behalf Of John Fox
> Sent: January-04-11 4:36 PM
> To: r-devel at 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 at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

peter dalgaard

2011-Jan-04 23:04 UTC

head link

[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.mes at cbs.dk  Priv: PDalgd at gmail.com

Gabor Grothendieck

2011-Jan-04 23:56 UTC

head link

[Rd] scoping/non-standard evaluation issue

On Tue, Jan 4, 2011 at 4:35 PM, John Fox <jfox at 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

Kenn Konstabel

2011-Jan-06 12:11 UTC

head link

[Rd] scoping/non-standard evaluation issue

the following seems an easy solution:

f1 <- function(mod){
     subs <- 1:10
     toeval <- quote(update(mod, subset=subs))
     toeval$subset<-subs
     eval(toeval)
     }

f1(mod.2)

When experimenting with this I once had (by mistake):

mod.2 <- lm(update(mod.1, . ~ . - Year + Year)) # instead of just
update(this)

... and this helped, too, i.e. f(mod.2) worked.


Best regards,
Kenn

Kenn Konstabel
Department of Chronic Diseases
National Institute for Health Development
Hiiu 42
Tallinn, Estonia

On Tue, Jan 4, 2011 at 11:35 PM, John Fox <jfox@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?
>
> 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
>
	[[alternative HTML version deleted]]

peter dalgaard

2011-Jan-06 12:31 UTC

head link

[Rd] scoping/non-standard evaluation issue

On Jan 6, 2011, at 13:11 , Kenn Konstabel wrote:
> the following seems an easy solution:
> 
> f1 <- function(mod){
>     subs <- 1:10
>     toeval <- quote(update(mod, subset=subs))
>     toeval$subset<-subs
>     eval(toeval)
>     }
> 
> f1(mod.2)
Tere, Kenn!

Yes, enforcing pass-by-value by pre-evaluating the argument will certainly
defeat the nonstandard evaluation issues. Another version of the same idea is

eval(bquote(update(mod, .(subs)))

The only thing is that if the argument is ever deparsed, you might get a messy
display. E.g., try eval(bquote(plot(.(rnorm(20)))))

-pd

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

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