[Rd] round.Date and trunc.Date not working / implemented

[Rui Barradas]

Às 14:36 de 08/02/2024, Olivier Benz via R-devel escreveu:
>> On 8 Feb 2024, at 15:15, Martin Maechler <maechler using stat.math.ethz.ch> wrote:
>>
>>>>>>> Jiří 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
> 
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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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