[R] Unintended behaviour of stats::time not returning integers for the first cycle

[Jeff Newmiller]

> did not know which mailing list to write to.

... then you did not read the Posting Guide, or forgot to refer to it?

On October 18, 2022 5:26:28 AM PDT, "Andreï V. Kostyrka" <andrei.kostyrka using gmail.com> wrote:
>Sure, this works, and I was thinking about this solution, but it seems like
>a dirty one-time trick. I was wondering whether the following 3 lines could
>be considered for inclusion by the core developers, but did not know which
>mailing list to write to. Here is my proposal:
>
>correctTime <- function (x, offset = 0, ...) { # Changes
>stats:::time.default
>  n <- if (is.matrix(x)) nrow(x) else length(x)
>  xtsp <- attr(hasTsp(x), "tsp")
>  y <- seq.int(xtsp[1L], xtsp[2L], length.out = n) + offset/xtsp[3L]
>  round.y <- round(y)
>  near.integer <- abs(round.y - y) < sqrt(.Machine$double.eps)
>  y[near.integer] <- round.y[near.integer]
>  tsp(y) <- xtsp
>  y
>}
>
>x <- ts(2:252, start = c(2002, 2), freq = 12)
>d <- seq.Date(as.Date("2002-02-01"), to = as.Date("2022-12-01"), by =
>"month")
>true.year <- rep(2002:2022, each = 12)[-1]
>wrong.year <- floor(as.numeric(time(x)))
>print(as.numeric(time(x))[240], 20) # 2021.9999999999997726, the floor of
>which is 2021
>print(correctTime(x)[240], 20) # 2022
>
>On Sat, Oct 15, 2022 at 11:56 AM Eric Berger <ericjberger using gmail.com> wrote:
>
>> Alternatively
>>
>> correct.year <- floor(time(x)+1e-6)
>>
>> On Sat, Oct 15, 2022 at 10:26 AM Andreï V. Kostyrka <
>> andrei.kostyrka using gmail.com> wrote:
>>
>>> Dear all,
>>>
>>>
>>>
>>> I was using stats::time to obtain the year as a floor of it, and
>>> encountered a problem: due to a rounding error (most likely due to its
>>> reliance on the base::seq.int internally, but correct me if I am wrong),
>>> the actual number corresponding to the beginning of a year X can still be
>>> (X-1).9999999..., resulting in the following undesirable behaviour.
>>>
>>>
>>>
>>> One of the simplest ways of getting the year from a ts object is
>>> floor(time(...)). However, if the starting time cannot be represented
>>> nicely as a power of 2, then, supposedly integer time does not have a
>>> .000000... mantissa:
>>>
>>>
>>>
>>> x <- ts(2:252, start = c(2002, 2), freq = 12)
>>>
>>> d <- seq.Date(as.Date("2002-02-01"), to = as.Date("2022-12-01"), by =
>>> "month")
>>>
>>> true.year <- rep(2002:2022, each = 12)[-1]
>>>
>>> wrong.year <- floor(as.numeric(time(x)))
>>>
>>> tail(cbind(as.character(d), true.year, wrong.year), 15) # Look at
>>> 2022-01-01
>>>
>>> print(as.numeric(time(x))[240], 20) # 2021.9999999999997726, the floor of
>>> which is 2021
>>>
>>>
>>>
>>> Yes, I have read the 'R inferno' book and know the famous '0.3 != 0.7 -
>>> 0.4' example, but I believe that the expected / intended behaviour would
>>> be
>>> actually returning round years for the first observation in a year. This
>>> could be achieved by rounding the near-integer time to integers.
>>>
>>>
>>>
>>> Since users working with dates are expecting to get exact integer years
>>> for
>>> the first cycle of a ts, this should be changed. Thank you in advance for
>>> considering a fix.
>>>
>>>
>>>
>>> Yours sincerely,
>>>
>>> Andreï V. Kostyrka
>>>
>>>         [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

-- 
Sent from my phone. Please excuse my brevity.