Dear Bert, I'm tempted to let this thread drop, since I like your last solution better than mine: it's clearer and more robust -- in fact, I don't see a way to break it -- and the approach you used to write it generalizes better to other problems. But if the object is to produce a function that behaves like deparse(substitute()), which is the subject of the original posting, then
> g <- function(x) deparse(substitute(x)) > h <- function(foo) g(foo) > h(log) [1] "foo" Best, John > -----Original Message----- > From: Bert Gunter [mailto:bgunter.4...@gmail.com] > Sent: December 13, 2016 12:52 AM > To: Fox, John <j...@mcmaster.ca> > Cc: frede...@ofb.net; r-help@r-project.org > Subject: Re: [R] how do I define a function which is equivalent to > `deparse(substitute(x))`? > > John: > > If you insist: > > > desub <- function(x) > deparse(sys.call(-length(sys.parents())+1)[[2]]) > > > > > f <- function(y)desub(y) > > g <- function(y)message(desub(y)) > > > > f(log) > [1] "log" > > > g(log) > log > > > However, I would agree that searching backward through the call stack can be > tricky. For example, suppose we have in addition to the above, > > h <- function(foo) g(foo) > > Then using desub() as I defined it above, one gets as desired: > > > h(log) > log > > However, using your gsub(), > > > desub <- function(y) { > deparse(eval(substitute(substitute(y)), > env=parent.frame())) > } > > One then gets: > > > h(log) > foo ## whoops! > > I suspect one can find a way to break my approach that doesn't break yours -- > and if/when you find it, please post it. But on general principles I prefer > accessing the call stack directly rather than indirectly through nested > substitute > calls. But beauty is in the eye of the beholder... > > > Cheers, > Bert > > > > > > 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 5:45 PM, Fox, John <j...@mcmaster.ca> wrote: > > 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.4...@gmail.com] > >> Sent: December 12, 2016 7:26 PM > >> To: Fox, John <j...@mcmaster.ca> > >> Cc: frede...@ofb.net; r-help@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 <j...@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.4...@gmail.com] > >> >> Sent: Monday, December 12, 2016 6:41 PM > >> >> To: Fox, John <j...@mcmaster.ca> > >> >> Cc: frede...@ofb.net; r-help@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 <j...@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-boun...@r-project.org] On Behalf Of > >> >> >> frede...@ofb.net > >> >> >> Sent: December 11, 2016 8:35 PM > >> >> >> To: r-help@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, frede...@ofb.net wrote: > >> >> >> > >Dear R-Help, > >> >> >> > > > >> >> >> > >I asked this question on StackOverflow, > >> >> >> > > > >> >> >> > >http://stackoverflow.com/questions/41083293/in-r-how-do-i-de > >> >> >> > >fin 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@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@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@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@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.
