R devel - Feb 2024 - round.Date and trunc.Date not working / implemented

?s 14:36 de 08/02/2024, Olivier Benz via R-devel
escreveu:
>> On 8 Feb 2024, at 15:15, Martin Maechler <maechler at
stat.math.ethz.ch> wrote:
>>
>>>>>>> Ji?? Moravec
>>>>>>>     on Wed, 7 Feb 2024 10:23:15 +1300 writes:
>>
>>> This is my first time working with dates, so if the answer is
"Duh, work
>>> with POSIXt", please ignore it.
>>
>>> Why is not `round.Date` and `trunc.Date` "implemented"
for `Date`?
>>
>>> Is this because `Date` is (mostly) a virtual class setup for a
better
>>> inheritance or is that something that is just missing? (like
>>> `sort.data.frame`). Would R core welcome a patch?
>>
>>> I decided to convert some dates to date using `as.Date` function,
which
>>> converts to a plain `Date` class, because that felt natural.
>>
>>> But then when trying to round to closest year, I have realized that
the
>>> `round` and `trunc` for `Date` do not behave as for `POSIXt`.
>>
>>> I would assume that these will have equivalent output:
>>
>>> Sys.time() |> round("years") # 2024-01-01 NZDT
>>
>>> Sys.Date() |> round("years") # Error in
round.default(...): non-numeric
>>> argument to mathematical function
>>
>>
>>> Looking at the code (and reading the documentation more carefully)
shows
>>> the issue, but this looks like an omission that should be patched.
>>
>>> -- Jirka
>>
>> You are wrong:  They *are* implemented,
>> both even visible since they are in the 'base' package!
>>
>> ==> they have help pages you can read ....
>>
>> Here are examples:
>>
>>> trunc(Sys.Date())
>> [1] "2024-02-08"
>>> trunc(Sys.Date(), "month")
>> [1] "2024-02-01"
>>> trunc(Sys.Date(), "year")
>> [1] "2024-01-01"
>>>
>>
> 
> Maybe he meant
> 
> r$> Sys.time() |> round.POSIXt("years")
> [1] "2024-01-01 CET"
> 
> r$> Sys.Date() |> round.POSIXt("years")
> [1] "2024-01-01 UTC"
> 
> The only difference is the timezone
> 
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
Hello,

You are right that the timezones are different but Sys.date() returns an 
object of class "Date" so the method called is not that one.
Here an example with trunc.


Sys.Date() |> class()
Sys.Date() |> trunc("years")
Sys.Date() |> trunc.Date("years")
Sys.Date() |> trunc.POSIXt("years")


As for the OP, the problem is thhat the generic roun())) doesn't have 
unit argument. So I am  nnnot understanding why round.POSIXt works.


Sys.Date() |> round("years")
#> Error in round.default(structure(19761, class = "Date"),
"years"):
non-numeric argument to mathematical function
Sys.Date() |> round.Date("years")
#> Error in NextMethod(): generic function not specified

Sys.Date() |> round.POSIXt("years")
#> [1] "2024-01-01 UTC"
Sys.Date() |> round.POSIXt("months")
#> [1] "2024-02-01 UTC"
Sys.Date() |> round.POSIXt("days")
#> [1] "2024-02-08 UTC"


Hope this helps,

Rui Barradas



-- 
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Technically, there is a round() for 'Date' objects, but it doesn't
seem very useful, because it basically just fall back to the default
round() method, which only takes the 'digits' argument.

Here's an example:
> date <- Sys.Date()
> class(date)
[1] "Date"

We see that there are only two round() methods in addition to the
implicit built-in one;
> methods("round")
[1] round.Date   round.POSIXt
see '?methods' for accessing help and source code

Looking at round() for 'Date';
> round.Date
function (x, ...)
{
    .Date(NextMethod(), oldClass(x))
}
<environment: namespace:base>

we see that it defers to the next method here, which is the built-in
one. The built-in one, only accepts 'digits', which does nothing for
digits >= 0.  For digits < 0, it rounds to power of ten, e.g.
> date
[1] "2024-02-08"
> round(date, digits = 0)
[1] "2024-02-08"
> round(date, digits = 1)
[1] "2024-02-08"
> round(date, digits = 2)
[1] "2024-02-08"
> round(date, digits = -1)
[1] "2024-02-07"
> round(date, digits = -2)
[1] "2024-03-18"
> round(date, digits = -3)
[1] "2024-10-04"
> round(date, digits = -4)
[1] "2024-10-04"
> round(date, digits = -5)
[1] "1970-01-01"

So, although technically invalid, OPs remark is a valid one. I'd also
expect `round()` for Date to support 'units' similar to timestamps,
e.g.
> time <- Sys.time()
> class(time)
[1] "POSIXct" "POSIXt"
> time
[1] "2024-02-08 09:17:02 PST"
> round(time, units = "days")
[1] "2024-02-08 PST"
> round(time, units = "months")
[1] "2024-02-01 PST"
> round(time, units = "years")
[1] "2024-01-01 PST"

So, I agree with OP that one would expect:
> round(date, units = "days")
[1] "2024-02-08"
> round(date, units = "months")
[1] "2024-02-01"
> round(date, units = "years")
[1] "2024-01-01"

to also work here.

FWIW, I don't think we want to encourage circumventing the S3 generic
and calling S3 methods directly, i.e. I don't recommend doing things
like round.POSIXt(...). Ideally, all S3 methods in R would be
non-exported, but some remain exported for legacy reason. But, I think
we should treat them as if they in the future will become
non-exported.

/Henrik

On Thu, Feb 8, 2024 at 8:18?AM Olivier Benz via R-devel
<r-devel at r-project.org> wrote:
>
> > On 8 Feb 2024, at 15:15, Martin Maechler <maechler at
stat.math.ethz.ch> wrote:
> >
> >>>>>> Ji?? Moravec
> >>>>>>    on Wed, 7 Feb 2024 10:23:15 +1300 writes:
> >
> >> This is my first time working with dates, so if the answer is
"Duh, work
> >> with POSIXt", please ignore it.
> >
> >> Why is not `round.Date` and `trunc.Date` "implemented"
for `Date`?
> >
> >> Is this because `Date` is (mostly) a virtual class setup for a
better
> >> inheritance or is that something that is just missing? (like
> >> `sort.data.frame`). Would R core welcome a patch?
> >
> >> I decided to convert some dates to date using `as.Date` function,
which
> >> converts to a plain `Date` class, because that felt natural.
> >
> >> But then when trying to round to closest year, I have realized
that the
> >> `round` and `trunc` for `Date` do not behave as for `POSIXt`.
> >
> >> I would assume that these will have equivalent output:
> >
> >> Sys.time() |> round("years") # 2024-01-01 NZDT
> >
> >> Sys.Date() |> round("years") # Error in
round.default(...): non-numeric
> >> argument to mathematical function
> >
> >
> >> Looking at the code (and reading the documentation more carefully)
shows
> >> the issue, but this looks like an omission that should be patched.
> >
> >> -- Jirka
> >
> > You are wrong:  They *are* implemented,
> > both even visible since they are in the 'base' package!
> >
> > ==> they have help pages you can read ....
> >
> > Here are examples:
> >
> >> trunc(Sys.Date())
> > [1] "2024-02-08"
> >> trunc(Sys.Date(), "month")
> > [1] "2024-02-01"
> >> trunc(Sys.Date(), "year")
> > [1] "2024-01-01"
> >>
> >
>
> Maybe he meant
>
> r$> Sys.time() |> round.POSIXt("years")
> [1] "2024-01-01 CET"
>
> r$> Sys.Date() |> round.POSIXt("years")
> [1] "2024-01-01 UTC"
>
> The only difference is the timezone
>
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
On Thu, Feb 8, 2024 at 9:06?AM Rui Barradas <ruipbarradas at sapo.pt>
wrote:
>
> ?s 14:36 de 08/02/2024, Olivier Benz via R-devel escreveu:
> >> On 8 Feb 2024, at 15:15, Martin Maechler <maechler at
stat.math.ethz.ch> wrote:
> >>
> >>>>>>> Ji?? Moravec
> >>>>>>>     on Wed, 7 Feb 2024 10:23:15 +1300 writes:
> >>
> >>> This is my first time working with dates, so if the answer is
"Duh, work
> >>> with POSIXt", please ignore it.
> >>
> >>> Why is not `round.Date` and `trunc.Date`
"implemented" for `Date`?
> >>
> >>> Is this because `Date` is (mostly) a virtual class setup for a
better
> >>> inheritance or is that something that is just missing? (like
> >>> `sort.data.frame`). Would R core welcome a patch?
> >>
> >>> I decided to convert some dates to date using `as.Date`
function, which
> >>> converts to a plain `Date` class, because that felt natural.
> >>
> >>> But then when trying to round to closest year, I have realized
that the
> >>> `round` and `trunc` for `Date` do not behave as for `POSIXt`.
> >>
> >>> I would assume that these will have equivalent output:
> >>
> >>> Sys.time() |> round("years") # 2024-01-01 NZDT
> >>
> >>> Sys.Date() |> round("years") # Error in
round.default(...): non-numeric
> >>> argument to mathematical function
> >>
> >>
> >>> Looking at the code (and reading the documentation more
carefully) shows
> >>> the issue, but this looks like an omission that should be
patched.
> >>
> >>> -- Jirka
> >>
> >> You are wrong:  They *are* implemented,
> >> both even visible since they are in the 'base' package!
> >>
> >> ==> they have help pages you can read ....
> >>
> >> Here are examples:
> >>
> >>> trunc(Sys.Date())
> >> [1] "2024-02-08"
> >>> trunc(Sys.Date(), "month")
> >> [1] "2024-02-01"
> >>> trunc(Sys.Date(), "year")
> >> [1] "2024-01-01"
> >>>
> >>
> >
> > Maybe he meant
> >
> > r$> Sys.time() |> round.POSIXt("years")
> > [1] "2024-01-01 CET"
> >
> > r$> Sys.Date() |> round.POSIXt("years")
> > [1] "2024-01-01 UTC"
> >
> > The only difference is the timezone
> >
> >> ______________________________________________
> >> R-devel at r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> > ______________________________________________
> > R-devel at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-devel
> Hello,
>
> You are right that the timezones are different but Sys.date() returns an
> object of class "Date" so the method called is not that one.
> Here an example with trunc.
>
>
> Sys.Date() |> class()
> Sys.Date() |> trunc("years")
> Sys.Date() |> trunc.Date("years")
> Sys.Date() |> trunc.POSIXt("years")
>
>
> As for the OP, the problem is thhat the generic roun())) doesn't have
> unit argument. So I am  nnnot understanding why round.POSIXt works.
>
>
> Sys.Date() |> round("years")
> #> Error in round.default(structure(19761, class = "Date"),
"years"):
> non-numeric argument to mathematical function
> Sys.Date() |> round.Date("years")
> #> Error in NextMethod(): generic function not specified
>
> Sys.Date() |> round.POSIXt("years")
> #> [1] "2024-01-01 UTC"
> Sys.Date() |> round.POSIXt("months")
> #> [1] "2024-02-01 UTC"
> Sys.Date() |> round.POSIXt("days")
> #> [1] "2024-02-08 UTC"
>
>
> Hope this helps,
>
> Rui Barradas
>
>
>
> --
> Este e-mail foi analisado pelo software antiv?rus AVG para verificar a
presen?a de v?rus.
> www.avg.com
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel