From m@ech|er @end|ng |rom @t@t@m@th@ethz@ch  Thu May 11 10:49:49 2023
From: m@ech|er @end|ng |rom @t@t@m@th@ethz@ch (Martin Maechler)
Date: Thu, 11 May 2023 10:49:49 +0200
Subject: [Rd] range() for Date and POSIXct could respect `finite = TRUE`
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Message-ID: <25692.44077.542251.477187@stat.math.ethz.ch>

>>>>> Davis Vaughan 
>>>>>     on Tue, 9 May 2023 09:49:41 -0400 writes:

    > It seems like the main problem is that `is.numeric(x)`
    > isn't fully indicative of whether or not `is.finite(x)`
    > makes sense for `x` (i.e.  Date isn't numeric but does
    > allow infinite dates).

    > So I could also imagine a new `allows.infinite()` S3
    > generic that would return a single TRUE/FALSE for whether
    > or not the type allows infinite values, this would also be
    > indicative of whether or not `is.finite()` and
    > `is.infinite()` make sense on that type. I imagine it
    > being used like:

> ```
>   allows.infinite <- function(x) {
>     UseMethod("allows.infinite")
>   }
>   allows.infinite.default <- function(x) {
>     is.numeric(x) # For backwards compatibility, maybe? Not sure.
>   }
>   allows.infinite.Date <- function(x) {
>     TRUE
>   }
>   allows.infinite.POSIXct <- function(x) {
>     TRUE
>   }
>
>   range.default <- function (..., na.rm = FALSE, finite = FALSE) {
>     x <- c(..., recursive = TRUE)
>     if (allows.infinite(x)) { # changed from `is.numeric()`
>	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))
>     }
>   }
>   ```

    > It could allow other R developers to also use the pattern of:

    > ```
    > if (allows.infinite(x)) {
    >    # conditionally do stuff with is.infinite(x)
    > }
    > ```

    > and that seems like it could be rather nice.

    > It would avoid the need for `range.Date()` and `range.POSIXct()` methods too.

    > -Davis

That *is* an interesting alternative perspective ...
sent just about before I was going to commit my proposal (incl
new help page entries, regr.tests ..).

So we would introduce a new generic  allows.infinite() {or
better name?,  allowsInf, ..} with the defined semantic that

allows.infinite(x) for a vector 'x' gives a logical "scalar",
TRUE iff it is known that  is.finite(x) "makes sense" and
returns a logical vector of length length(x) .. which is TRUE
where x[i] is not NA/NaN/+Inf/-Inf .. *and*
is.infinite := Negate(is.finite)    {or vice versa if you prefer}.

I agree that this may be useful somewhat more generally than
just for  range() methods.

What do others think?

Martin


    > On Thu, May 4, 2023 at 5:29?AM Martin Maechler
    > <maechler at stat.math.ethz.ch> wrote:
[......]

    >> >>>>> 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 at 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
    >> >>
    >> >> > ______________________________________________
    >> >> > R-devel at r-project.org mailing list
    >> >> > https://stat.ethz.ch/mailman/listinfo/r-devel



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