[Rd] [External] Re: New pipe operator
iuke-tier@ey m@iii@g oii uiow@@edu
iuke-tier@ey m@iii@g oii uiow@@edu
Sun Dec 6 19:09:13 CET 2020
On Sun, 6 Dec 2020, Gabor Grothendieck wrote:
> The following gives an error.
>
> 1 |> `+`(2)
> ## Error: function '+' is not supported in RHS call of a pipe
>
> 1 |> `+`()
> ## Error: function '+' is not supported in RHS call of a pipe
>
> but this does work:
>
> 1 |> (`+`)(2)
> ## [1] 3
>
> 1 |> (`+`)()
> ## [1] 1
>
> The error message suggests that this was intentional.
> It isn't mentioned in ?"|>"
?"|>" says:
To avoid ambiguities, functions in ‘rhs’ calls may not
be syntactically special, such as ‘+’ or ‘if’.
(used to say lhs; fixed now).
Best,
luke
>
> On Sat, Dec 5, 2020 at 1:19 PM <luke-tierney using uiowa.edu> wrote:
>>
>> We went back and forth on this several times. The key advantage of
>> requiring parentheses is to keep things simple and consistent. Let's
>> get some experience with that. If experience shows requiring
>> parentheses creates too many issues then we can add the option of
>> dropping them later (with special handling of :: and :::). It's easier
>> to add flexibility and complexity than to restrict it after the fact.
>>
>> Best,
>>
>> luke
>>
>> On Sat, 5 Dec 2020, Hugh Parsonage wrote:
>>
>>> I'm surprised by the aversion to
>>>
>>> mtcars |> nrow
>>>
>>> over
>>>
>>> mtcars |> nrow()
>>>
>>> and I think the decision to disallow the former should be
>>> reconsidered. The pipe operator is only going to be used when the rhs
>>> is a function, so there is no ambiguity with omitting the parentheses.
>>> If it's disallowed, it becomes inconsistent with other treatments like
>>> sapply(mtcars, typeof) where sapply(mtcars, typeof()) would just be
>>> noise. I'm not sure why this decision was taken
>>>
>>> If the only issue is with the double (and triple) colon operator, then
>>> ideally `mtcars |> base::head` should resolve to `base::head(mtcars)`
>>> -- in other words, demote the precedence of |>
>>>
>>> Obviously (looking at the R-Syntax branch) this decision was
>>> considered, put into place, then dropped, but I can't see why
>>> precisely.
>>>
>>> Best,
>>>
>>>
>>> Hugh.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Sat, 5 Dec 2020 at 04:07, Deepayan Sarkar <deepayan.sarkar using gmail.com> wrote:
>>>>
>>>> On Fri, Dec 4, 2020 at 7:35 PM Duncan Murdoch <murdoch.duncan using gmail.com> wrote:
>>>>>
>>>>> On 04/12/2020 8:13 a.m., Hiroaki Yutani wrote:
>>>>>>> Error: function '::' not supported in RHS call of a pipe
>>>>>>
>>>>>> To me, this error looks much more friendly than magrittr's error.
>>>>>> Some of them got too used to specify functions without (). This
>>>>>> is OK until they use `::`, but when they need to use it, it takes
>>>>>> hours to figure out why
>>>>>>
>>>>>> mtcars %>% base::head
>>>>>> #> Error in .::base : unused argument (head)
>>>>>>
>>>>>> won't work but
>>>>>>
>>>>>> mtcars %>% head
>>>>>>
>>>>>> works. I think this is a too harsh lesson for ordinary R users to
>>>>>> learn `::` is a function. I've been wanting for magrittr to drop the
>>>>>> support for a function name without () to avoid this confusion,
>>>>>> so I would very much welcome the new pipe operator's behavior.
>>>>>> Thank you all the developers who implemented this!
>>>>>
>>>>> I agree, it's an improvement on the corresponding magrittr error.
>>>>>
>>>>> I think the semantics of not evaluating the RHS, but treating the pipe
>>>>> as purely syntactical is a good decision.
>>>>>
>>>>> I'm not sure I like the recommended way to pipe into a particular argument:
>>>>>
>>>>> mtcars |> subset(cyl == 4) |> \(d) lm(mpg ~ disp, data = d)
>>>>>
>>>>> or
>>>>>
>>>>> mtcars |> subset(cyl == 4) |> function(d) lm(mpg ~ disp, data = d)
>>>>>
>>>>> both of which are equivalent to
>>>>>
>>>>> mtcars |> subset(cyl == 4) |> (function(d) lm(mpg ~ disp, data = d))()
>>>>>
>>>>> It's tempting to suggest it should allow something like
>>>>>
>>>>> mtcars |> subset(cyl == 4) |> lm(mpg ~ disp, data = .)
>>>>
>>>> Which is really not that far off from
>>>>
>>>> mtcars |> subset(cyl == 4) |> \(.) lm(mpg ~ disp, data = .)
>>>>
>>>> once you get used to it.
>>>>
>>>> One consequence of the implementation is that it's not clear how
>>>> multiple occurrences of the placeholder would be interpreted. With
>>>> magrittr,
>>>>
>>>> sort(runif(10)) %>% ecdf(.)(.)
>>>> ## [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
>>>>
>>>> This is probably what you would expect, if you expect it to work at all, and not
>>>>
>>>> ecdf(sort(runif(10)))(sort(runif(10)))
>>>>
>>>> There would be no such ambiguity with anonymous functions
>>>>
>>>> sort(runif(10)) |> \(.) ecdf(.)(.)
>>>>
>>>> -Deepayan
>>>>
>>>>> which would be expanded to something equivalent to the other versions:
>>>>> but that makes it quite a bit more complicated. (Maybe _ or \. should
>>>>> be used instead of ., since those are not legal variable names.)
>>>>>
>>>>> I don't think there should be an attempt to copy magrittr's special
>>>>> casing of how . is used in determining whether to also include the
>>>>> previous value as first argument.
>>>>>
>>>>> Duncan Murdoch
>>>>>
>>>>>
>>>>>>
>>>>>> Best,
>>>>>> Hiroaki Yutani
>>>>>>
>>>>>> 2020年12月4日(金) 20:51 Duncan Murdoch <murdoch.duncan using gmail.com>:
>>>>>>>
>>>>>>> Just saw this on the R-devel news:
>>>>>>>
>>>>>>>
>>>>>>> R now provides a simple native pipe syntax ‘|>’ as well as a shorthand
>>>>>>> notation for creating functions, e.g. ‘\(x) x + 1’ is parsed as
>>>>>>> ‘function(x) x + 1’. The pipe implementation as a syntax transformation
>>>>>>> was motivated by suggestions from Jim Hester and Lionel Henry. These
>>>>>>> features are experimental and may change prior to release.
>>>>>>>
>>>>>>>
>>>>>>> This is a good addition; by using "|>" instead of "%>%" there should be
>>>>>>> a chance to get operator precedence right. That said, the ?Syntax help
>>>>>>> topic hasn't been updated, so I'm not sure where it fits in.
>>>>>>>
>>>>>>> There are some choices that take a little getting used to:
>>>>>>>
>>>>>>> > mtcars |> head
>>>>>>> Error: The pipe operator requires a function call or an anonymous
>>>>>>> function expression as RHS
>>>>>>>
>>>>>>> (I need to say mtcars |> head() instead.) This sometimes leads to error
>>>>>>> messages that are somewhat confusing:
>>>>>>>
>>>>>>> > mtcars |> magrittr::debug_pipe |> head
>>>>>>> Error: function '::' not supported in RHS call of a pipe
>>>>>>>
>>>>>>> but
>>>>>>>
>>>>>>> mtcars |> magrittr::debug_pipe() |> head()
>>>>>>>
>>>>>>> works.
>>>>>>>
>>>>>>> Overall, I think this is a great addition, though it's going to be
>>>>>>> disruptive for a while.
>>>>>>>
>>>>>>> Duncan Murdoch
>>>>>>>
>>>>>>> ______________________________________________
>>>>>>> R-devel using r-project.org mailing list
>>>>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>>>>
>>>>>> ______________________________________________
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>>>>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>>>>
>>>>>
>>>>> ______________________________________________
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>>
>> --
>> Luke Tierney
>> Ralph E. Wareham Professor of Mathematical Sciences
>> University of Iowa Phone: 319-335-3386
>> Department of Statistics and Fax: 319-335-3017
>> Actuarial Science
>> 241 Schaeffer Hall email: luke-tierney using uiowa.edu
>> Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
>> ______________________________________________
>> R-devel using r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
>
>
--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tierney using uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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