[Rd] range() for Date and POSIXct could respect `finite = TRUE`

[Tim Taylor]

A tiny nit-pick nit-pick: I'd take NA to mean the finish date is missing 
and you know neither whether the event has finished or if it has 
finished at all :-)

Either way the proposed method seems sensible.

Tim

On 28/04/2023 16:29, Paul McQuesten wrote:
> A tiny nit-pick: Seems to me that end date = NA would mean the event has
> not yet ended, whilst Inf would mean that the event is known to never
> terminate, ie: an eternal fact, or physical law.
>
> On Fri, Apr 28, 2023 at 10:12 AM Davis Vaughan via R-devel <
> r-devel using r-project.org> wrote:
>
>> Hi all,
>>
>> I noticed that `range.default()` has a nice `finite = TRUE` argument,
>> but it doesn't actually apply to Date or POSIXct due to how
>> `is.numeric()` works.
>>
>> ```
>> x <- .Date(c(0, Inf, 1, 2, Inf))
>> x
>> #> [1] "1970-01-01" "Inf"        "1970-01-02" "1970-01-03" "Inf"
>>
>> # Darn!
>> range(x, finite = TRUE)
>> #> [1] "1970-01-01" "Inf"
>>
>> # What I want
>> .Date(range(unclass(x), finite = TRUE))
>> #> [1] "1970-01-01" "1970-01-03"
>> ```
>>
>> I think `finite = TRUE` would be pretty nice for Dates in particular.
>>
>> As a motivating example, sometimes you have ranges of dates
>> represented by start/end pairs. It is fairly natural to represent an
>> event that hasn't ended yet with an infinite date. If you need to then
>> compute a sequence of dates spanning the full range of the start/end
>> pairs, it would be nice to be able to use `range(finite = TRUE)` to do
>> so:
>>
>> ```
>> start <- as.Date(c("2019-01-05", "2019-01-10", "2019-01-11", "2019-01-14"))
>> end <- as.Date(c("2019-01-07", NA, "2019-01-14", NA))
>> end[is.na(end)] <- Inf
>>
>> # `end = Inf` means that the event hasn't "ended" yet
>> data.frame(start, end)
>> #>        start        end
>> #> 1 2019-01-05 2019-01-07
>> #> 2 2019-01-10        Inf
>> #> 3 2019-01-11 2019-01-14
>> #> 4 2019-01-14        Inf
>>
>> # Create a full sequence along all days in start/end
>> range <- .Date(range(unclass(c(start, end)), finite = TRUE))
>> seq(range[1], range[2], by = 1)
>> #>  [1] "2019-01-05" "2019-01-06" "2019-01-07" "2019-01-08" "2019-01-09"
>> #>  [6] "2019-01-10" "2019-01-11" "2019-01-12" "2019-01-13" "2019-01-14"
>> ```
>>
>> It seems like one option is to create a `range.Date()` method that
>> unclasses, forwards the arguments on to a second call to `range()`,
>> and then reclasses?
>>
>> ```
>> range.Date <- function(x, ..., na.rm = FALSE, finite = FALSE) {
>>    .Date(range(unclass(x), na.rm = na.rm, finite = finite), oldClass(x))
>> }
>> ```
>>
>> This is similar to how `rep.Date()` works.
>>
>> Thanks,
>> Davis Vaughan
>>
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