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

[Paul McQuesten]

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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