[R] how do I define a function which is equivalent to `deparse(substitute(x))`?

Fox, John jfox at mcmaster.ca
Tue Dec 13 02:45:12 CET 2016 

Dear Bert,

Your current version satisfies the original posting, but, though simpler than mine, is a bit fragile, in the following sense:

> desub <- function(x) (all.vars(sys.call(-2)))

> f <- function(x){
+     message(desub(x))
+ }

> f(log)
log

> g <- function(x){
+     desub(x)
+ }

> g(log)
character(0)


My version:

> desub <- function(y) {
+     deparse(eval(substitute(substitute(y)), 
+                  env=parent.frame()))
+ }

> f(log)
log

> g(log)
[1] "log"

The deparse(substitute()) idiom returns the argument to f() or g() as a character string and so desub() should too, I guess.

Best,
 John

> -----Original Message-----
> From: Bert Gunter [mailto:bgunter.4567 at gmail.com]
> Sent: December 12, 2016 7:26 PM
> To: Fox, John <jfox at mcmaster.ca>
> Cc: frederik at ofb.net; r-help at r-project.org
> Subject: Re: [R] how do I define a function which is equivalent to
> `deparse(substitute(x))`?
> 
> John. et. al:
> 
> I assumed the message call was there to convert a quoted string to an
> unquoted name and simply did this with as.name() in desub(). The point of
> using sys.call() is that you can go up the call stack as far as you need, so if you
> want to leave in the message() call, just go one farther up the call stack:
> 
> > desub <- function(x) (all.vars(sys.call(-2))) ## note the -2 now
> 
> > g <- function(y)message((desub(y)))
> > g(log)
> log
> 
> 
> -- Bert
> 
> Bert Gunter
> 
> "The trouble with having an open mind is that people keep coming along and
> sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> 
> 
> On Mon, Dec 12, 2016 at 3:58 PM, Fox, John <jfox at mcmaster.ca> wrote:
> > Dear Bert,
> >
> > It's nitpicking, I guess, but the call to message() is in the original
> > posting. Your solution produces
> >
> >> desub <- function(x) as.name(all.vars(sys.call(-1)))
> >
> >> f <- function(x){
> > +     message(desub(x))
> > + }
> >
> >> f(log)
> > x
> >
> > Best,
> >  John
> >
> >> -----Original Message-----
> >> From: Bert Gunter [mailto:bgunter.4567 at gmail.com]
> >> Sent: Monday, December 12, 2016 6:41 PM
> >> To: Fox, John <jfox at mcmaster.ca>
> >> Cc: frederik at ofb.net; r-help at r-project.org
> >> Subject: Re: [R] how do I define a function which is equivalent to
> >> `deparse(substitute(x))`?
> >>
> >> *If* I understand correctly -- and please let me know if I don't --
> >> this seems somewhat more straightforward and less "hacky" :
> >>
> >> > desub <- function(x) as.name(all.vars(sys.call(-1)))
> >>
> >> Yielding in the OP's example:
> >>
> >> > g <- function(y)desub(y)
> >> > g(log)
> >> log
> >>
> >> Cheers,
> >> Bert
> >> Bert Gunter
> >>
> >> "The trouble with having an open mind is that people keep coming
> >> along and sticking things into it."
> >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >>
> >>
> >> On Mon, Dec 12, 2016 at 2:07 PM, Fox, John <jfox at mcmaster.ca> wrote:
> >> > Dear Frederick,
> >> >
> >> > I found this a challenging puzzle, and it took me awhile to come up
> >> with an alternative, and I think slightly simpler, solution:
> >> >
> >> >> desub <- function(y) {
> >> > +     deparse(eval(substitute(substitute(y)),
> >> > +                  env=parent.frame())) }
> >> >
> >> >> f <- function(x){
> >> > +     message(desub(x))
> >> > + }
> >> >
> >> >> f(log)
> >> > log
> >> >
> >> > Best,
> >> >  John
> >> >
> >> > -----------------------------
> >> > John Fox, Professor
> >> > McMaster University
> >> > Hamilton, Ontario
> >> > Canada L8S 4M4
> >> > Web: socserv.mcmaster.ca/jfox
> >> >
> >> >
> >> >
> >> >
> >> >> -----Original Message-----
> >> >> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of
> >> >> frederik at ofb.net
> >> >> Sent: December 11, 2016 8:35 PM
> >> >> To: r-help at r-project.org
> >> >> Subject: Re: [R] how do I define a function which is equivalent to
> >> >> `deparse(substitute(x))`?
> >> >>
> >> >> Dear R-Help,
> >> >>
> >> >> I was going to ask Jeff to read the entire works of William
> >> >> Shakespeare to learn why his reply was not helpful to me...
> >> >>
> >> >> Then I realized that the answer, as always, lies within...
> >> >>
> >> >>     desub <- function(y) {
> >> >>       e1=substitute(y, environment())
> >> >>       e2=do.call(substitute,list(e1), env=parent.frame())
> >> >>       deparse(e2)
> >> >>     }
> >> >>
> >> >> Sorry to trouble the list; other solutions still welcome.
> >> >>
> >> >> Cheers,
> >> >>
> >> >> Frederick
> >> >>
> >> >> On Sun, Dec 11, 2016 at 12:46:23AM -0800, Jeff Newmiller wrote:
> >> >> > No. Read Hadley Wickham's "Advanced R" to learn why not.
> >> >> > --
> >> >> > Sent from my phone. Please excuse my brevity.
> >> >> >
> >> >> > On December 10, 2016 10:24:49 PM PST, frederik at ofb.net wrote:
> >> >> > >Dear R-Help,
> >> >> > >
> >> >> > >I asked this question on StackOverflow,
> >> >> > >
> >> >> > >http://stackoverflow.com/questions/41083293/in-r-how-do-i-defin
> >> >> > >e-a -fu nction-which-is-equivalent-to-deparsesubstitutex
> >> >> > >
> >> >> > >but thought perhaps R-help would be more appropriate.
> >> >> > >
> >> >> > >I want to write a function in R which grabs the name of a
> >> >> > >variable from the context of its caller's caller. I think the
> >> >> > >problem I have is best understood by asking how to compose
> >> >> > >`deparse` and
> >> `substitute`.
> >> >> > >You can see that a naive composition does not work:
> >> >> > >
> >> >> > >    # a compose operator
> >> >> > >    >  `%c%` = function(x,y)function(...)x(y(...))
> >> >> > >
> >> >> > >    # a naive attempt to combine deparse and substitute
> >> >> > >    > desub = deparse %c% substitute
> >> >> > >    > f=function(foo) { message(desub(foo)) }
> >> >> > >    > f(log)
> >> >> > >    foo
> >> >> > >
> >> >> > >    # this is how it is supposed to work
> >> >> > >    > g=function(foo) { message(deparse(substitute(foo))) }
> >> >> > >    > g(log)
> >> >> > >    log
> >> >> > >
> >> >> > >Is there a way I can define a function `desub` so that
> >> >> > >`desub(x)` has the same value as `deparse(substitute(x))` in every
> context?
> >> >> > >
> >> >> > >Thank you,
> >> >> > >
> >> >> > >Frederick Eaton
> >> >> > >
> >> >> > >______________________________________________
> >> >> > >R-help at r-project.org mailing list -- To UNSUBSCRIBE and more,
> >> >> > >see https://stat.ethz.ch/mailman/listinfo/r-help
> >> >> > >PLEASE do read the posting guide
> >> >> > >http://www.R-project.org/posting-guide.html
> >> >> > >and provide commented, minimal, self-contained, reproducible code.
> >> >> >
> >> >>
> >> >> ______________________________________________
> >> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> >> PLEASE do read the posting guide
> >> >> http://www.R-project.org/posting-guide.html
> >> >> and provide commented, minimal, self-contained, reproducible code.
> >> >
> >> > ______________________________________________
> >> > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> > https://stat.ethz.ch/mailman/listinfo/r-help
> >> > PLEASE do read the posting guide
> >> > http://www.R-project.org/posting-guide.html
> >> > and provide commented, minimal, self-contained, reproducible code.

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