Re: [R] understanding as.list(substitute(...()))
> On 6 Oct 2020, at 09:22 , Dénes Tóth wrote:
>
> > foo <- function(...) substitute({...()})
> > foo(abc$de, fg[h], i)
> {
> pairlist(abc$de, fg[h], i)
> }
> > foo(abc$de, fg[h], , i) # add a missing argument for extra fun
> {
> as.pairlist(alist(abc$de, fg[h], , i))
> }
>
The 2nd one here is actually an artifact of deparse(). The result is still a
pairlist, just one that pairlist() cannot reproduce:
> e <- foo(abc$de, fg[h], , i)
> e[[2]]
[[1]]
abc$de
[[2]]
fg[h]
[[3]]
[[4]]
i
> deparse(e[[2]])
[1] "as.pairlist(alist(abc$de, fg[h], , i))"
> dput(e[[2]])
as.pairlist(alist(abc$de, fg[h], , i))
> mode(e[[2]])
[1] "pairlist"
> mode(e[[2]][[3]])
[1] "name"
I.e. the list in e[2] contains the missing indicator (an empty name). (I'm
slightly puzzled why we need the curlies to trigger a deparse, though)
--
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd@cbs.dk Priv: pda...@gmail.com
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Re: [R] understanding as.list(substitute(...()))
Cheers Denes,
That's useful to know. I'll stick with the match.call version
instead. Interestingly I initially tried to post to R-devel (as I
thought it may involve something internal) but was asked to post here
instead.
Best
Tim
On Tue, 6 Oct 2020 at 08:22, Dénes Tóth wrote:
>
> Hi Tim,
>
> I have also asked a similar question a couple of months ago, and someone
> else did the same recently, maybe on r-devel.
>
> We received no "official" response, but Deepayan Sarkar (R Core Team
> member) claimed that:
>
> "
> There is no documented reason for this to work (AFAIK), so again, I
> would guess this is a side-effect of the implementation, and not a API
> feature you should rely on. This is somewhat borne out by the
> following:
>
> > foo <- function(...) substitute({...()})
> > foo(abc$de, fg[h], i)
> {
> pairlist(abc$de, fg[h], i)
> }
> > foo(abc$de, fg[h], , i) # add a missing argument for extra fun
> {
> as.pairlist(alist(abc$de, fg[h], , i))
> }
>
> which is not something you would expect to see at the user level. So
> my recommendation: don't use ...() and pretend that you never
> discovered it in the first place. Use match.call() instead, as
> suggested by Serguei.
>
> [Disclaimer: I have no idea what is actually going on, so these are
> just guesses. There are some hints at
> https://cran.r-project.org/doc/manuals/r-devel/R-ints.html#Dot_002ddot_002ddot-arguments
> if you want to folllow up.]
> "
>
> Cheers,
> Denes
>
>
>
>
> On 10/6/20 8:38 AM, Tim Taylor wrote:
> > I probably need to be more specific. What confuses me is not the use
> > of substitute, but the parenthesis after the dots. It clearly works
> > and I can make guesses as to why but it is definitely not obvious.
> > The following function gives the same final result but I can
> > understand what is happening.
> >
> > dots <- function (...) {
> > exprs <- substitute(list(...))
> > as.list(exprs[-1])
> > }
> >
> > In the original, dots <- function(...) as.list(substitute(...())),
> > Does ...() get parsed in a special way?
> >
> > Tim
> >
> > On Tue, 6 Oct 2020 at 05:30, Bert Gunter wrote:
> >>
> >> You need to understand what substitute() does -- see ?substitute and/or a
> >> tutorial on "R computing on the language" or similar.
> >>
> >> Here is a simple example that may clarify:
> >>
> >>> dots <- function(...) as.list(substitute(...()))
> >>> dots(log(foo))
> >> [[1]]
> >> log(foo) ## a call, a language object
> >>
> >>> dots2 <- function(...) as.list(...)
> >>> dots2(log(foo))
> >> Error in as.list(...) : object 'foo' not found
> >> ## substitute() does not evaluate its argument; as.list() does
> >>
> >> Cheers,
> >> 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, Oct 5, 2020 at 1:37 PM Tim Taylor
> >> wrote:
> >>>
> >>> Could someone explain what is happening with the ...() of the
> >>> following function:
> >>>
> >>> dots <- function(...) as.list(substitute(...()))
> >>>
> >>> I understand what I'm getting as a result but not why. ?dots and
> >>> ?substitute leave me none the wiser.
> >>>
> >>> regards
> >>> Tim
> >>>
> >>> __
> >>> 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.
> >
__
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] understanding as.list(substitute(...()))
Hi Tim,
I have also asked a similar question a couple of months ago, and someone
else did the same recently, maybe on r-devel.
We received no "official" response, but Deepayan Sarkar (R Core Team
member) claimed that:
"
There is no documented reason for this to work (AFAIK), so again, I
would guess this is a side-effect of the implementation, and not a API
feature you should rely on. This is somewhat borne out by the
following:
> foo <- function(...) substitute({...()})
> foo(abc$de, fg[h], i)
{
pairlist(abc$de, fg[h], i)
}
> foo(abc$de, fg[h], , i) # add a missing argument for extra fun
{
as.pairlist(alist(abc$de, fg[h], , i))
}
which is not something you would expect to see at the user level. So
my recommendation: don't use ...() and pretend that you never
discovered it in the first place. Use match.call() instead, as
suggested by Serguei.
[Disclaimer: I have no idea what is actually going on, so these are
just guesses. There are some hints at
https://cran.r-project.org/doc/manuals/r-devel/R-ints.html#Dot_002ddot_002ddot-arguments
if you want to folllow up.]
"
Cheers,
Denes
On 10/6/20 8:38 AM, Tim Taylor wrote:
I probably need to be more specific. What confuses me is not the use
of substitute, but the parenthesis after the dots. It clearly works
and I can make guesses as to why but it is definitely not obvious.
The following function gives the same final result but I can
understand what is happening.
dots <- function (...) {
exprs <- substitute(list(...))
as.list(exprs[-1])
}
In the original, dots <- function(...) as.list(substitute(...())),
Does ...() get parsed in a special way?
Tim
On Tue, 6 Oct 2020 at 05:30, Bert Gunter wrote:
You need to understand what substitute() does -- see ?substitute and/or a tutorial on
"R computing on the language" or similar.
Here is a simple example that may clarify:
dots <- function(...) as.list(substitute(...()))
dots(log(foo))
[[1]]
log(foo) ## a call, a language object
dots2 <- function(...) as.list(...)
dots2(log(foo))
Error in as.list(...) : object 'foo' not found
## substitute() does not evaluate its argument; as.list() does
Cheers,
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, Oct 5, 2020 at 1:37 PM Tim Taylor
wrote:
Could someone explain what is happening with the ...() of the
following function:
dots <- function(...) as.list(substitute(...()))
I understand what I'm getting as a result but not why. ?dots and
?substitute leave me none the wiser.
regards
Tim
__
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and provide commented, minimal, self-contained, reproducible code.
__
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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
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] understanding as.list(substitute(...()))
I probably need to be more specific. What confuses me is not the use
of substitute, but the parenthesis after the dots. It clearly works
and I can make guesses as to why but it is definitely not obvious.
The following function gives the same final result but I can
understand what is happening.
dots <- function (...) {
exprs <- substitute(list(...))
as.list(exprs[-1])
}
In the original, dots <- function(...) as.list(substitute(...())),
Does ...() get parsed in a special way?
Tim
On Tue, 6 Oct 2020 at 05:30, Bert Gunter wrote:
>
> You need to understand what substitute() does -- see ?substitute and/or a
> tutorial on "R computing on the language" or similar.
>
> Here is a simple example that may clarify:
>
> > dots <- function(...) as.list(substitute(...()))
> > dots(log(foo))
> [[1]]
> log(foo) ## a call, a language object
>
> > dots2 <- function(...) as.list(...)
> > dots2(log(foo))
> Error in as.list(...) : object 'foo' not found
> ## substitute() does not evaluate its argument; as.list() does
>
> Cheers,
> 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, Oct 5, 2020 at 1:37 PM Tim Taylor
> wrote:
>>
>> Could someone explain what is happening with the ...() of the
>> following function:
>>
>> dots <- function(...) as.list(substitute(...()))
>>
>> I understand what I'm getting as a result but not why. ?dots and
>> ?substitute leave me none the wiser.
>>
>> regards
>> Tim
>>
>> __
>> 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.
Re: [R] understanding as.list(substitute(...()))
You need to understand what substitute() does -- see ?substitute and/or a tutorial on "R computing on the language" or similar. Here is a simple example that may clarify: > dots <- function(...) as.list(substitute(...())) > dots(log(foo)) [[1]] log(foo) ## a call, a language object > dots2 <- function(...) as.list(...) > dots2(log(foo)) Error in as.list(...) : object 'foo' not found ## substitute() does not evaluate its argument; as.list() does Cheers, 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, Oct 5, 2020 at 1:37 PM Tim Taylor wrote: > Could someone explain what is happening with the ...() of the > following function: > > dots <- function(...) as.list(substitute(...())) > > I understand what I'm getting as a result but not why. ?dots and > ?substitute leave me none the wiser. > > regards > Tim > > __ > 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. > [[alternative HTML version deleted]] __ 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] understanding as.list(substitute(...()))
Could someone explain what is happening with the ...() of the following function: dots <- function(...) as.list(substitute(...())) I understand what I'm getting as a result but not why. ?dots and ?substitute leave me none the wiser. regards Tim __ 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.
