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

[Martin Maechler]

>>>>> Davis Vaughan 
>>>>>     on Mon, 1 May 2023 08:46:33 -0400 writes:

    > Martin,
    > Yes, I missed that those have `Summary.*` methods, thanks!

    > Tweaking those to respect `finite = TRUE` sounds great. It seems like
    > it might be a little tricky since the Summary methods call
    > `NextMethod()`, and `range.default()` uses `is.numeric()` to determine
    > whether or not to apply `finite`. Because `is.numeric.Date()` is
    > defined, that always returns `FALSE` for Dates (and POSIXt). Because
    > of that, it may still be easier to just write a specific
    > `range.Date()` method, but I'm not sure.

    > -Davis

I've looked more closely now, and indeed,
range() is the only function in the  Summary  group
where (only) the default method has a 'finite' argument.
which strikes me as somewhat asymmetric / inconsequential, as
after all,  range(.) := c(min(.), max(.)) ,
but  min() and max() do not obey an finite=TRUE setting, note

> min(c(-Inf,3:5), finite=TRUE)
Error: attempt to use zero-length variable name

where the error message also is not particularly friendly
and of course has nothing to with 'finite' :

> max(1:4, foo="bar")
Error: attempt to use zero-length variable name
> 

... but that is diverting;  coming back to the topic:  Given
that 'finite' only applies to range() {and there is just a convenience},
I do agree that from my own work & support to make `Date` and
`POSIX(c)t` behave more number-like, it would be "nice" to have
range() obey a `finite=TRUE` also for these.

OTOH, there are quite a few other 'number-like' thingies for
which I would then like to have  range(*, finite=TRUE) work,
e.g.,  "mpfr" (package {Rmpfr}) or "bigz" {gmp} numbers, numeric
sparse matrices, ...

To keep such methods all internally consistent with
range.default(), I could envision something like this


.rangeNum <- function(..., na.rm = FALSE, finite = FALSE, isNumeric)
{
    x <- c(..., recursive = TRUE)
    if(isNumeric(x)) {
        if(finite) x <- x[is.finite(x)]
        else if(na.rm) x <- x[!is.na(x)]
	c(min(x), max(x))
    } else {
        if(finite) na.rm <- TRUE
        c(min(x, na.rm=na.rm), max(x, na.rm=na.rm))
    }
}

range.default <- function(..., na.rm = FALSE, finite = FALSE)
    .rangeNum(..., na.rm=na.rm, finite=finite, isNumeric = is.numeric)

range.POSIXct <- range.Date <- function(..., na.rm = FALSE, finite = FALSE)
    .rangeNum(..., na.rm=na.rm, finite=finite, isNumeric = function(.)TRUE)



which would also provide .rangeNum() to be used by implementors
of other numeric-like classes to provide their own range()
method as a 1-liner *and* be future-consistent with the default method..




    > On Sat, Apr 29, 2023 at 4:47 PM Martin Maechler
    > <maechler using stat.math.ethz.ch> wrote:
    >> 
    >> >>>>> Davis Vaughan via R-devel
    >> >>>>>     on Fri, 28 Apr 2023 11:12:27 -0400 writes:
    >> 
    >> > 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.
    >> 
    >> Well, I think it would / should never apply:
    >> 
    >> range() belongs to the "Summary" group generics (as min, max, ...)
    >> 
    >> and there  *are*  Summary.Date()  and Summary.POSIX{c,l}t() methods.
    >> 
    >> Without checking further for now, I think you are indirectly
    >> suggesting to enhance these three Summary.*() methods so they do
    >> obey  'finite = TRUE' .
    >> 
    >> I think I agree they should.
    >> 
    >> Martin
    >> 
    >> > ``` 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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