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

[Gabor Grothendieck]

The zoo package implements tolerances internally. Converting the ts
object to zoo:

  library(zoo)
  identical(as.integer(time(as.zoo(x))), true.year)
  ## [1] TRUE

On Sat, Oct 15, 2022 at 3:26 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]]
>
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