[R] Question about Date Object and time zones

[Kimmo Elo]

Hi,

I might have misunderstood your point, but why should a Date object 
store a timezone, since timezone is an attribute of time, not date?

Your tz-examples force R to present a timezone, resulting - this is my 
assumption - to default (=UTC) as there is no other information available.

Best,
Kimmo

Luca Brinkmann via R-help kirjoitti 24.9.2024 klo 17.10:
> Hello,
> 
> I have a question regarding the date objects and timezones. My current
> understanding is, that a Date object does only save the days from the
> origin and no more information about timezones or other information
> (please correct me if I am wrong).
> But if I use
> d = as.Date("2024-11-11")
> or
> d = as.Date("2024-11-11", tz="America/New_York")
> the date object is displayed in my RStudio environment as "2024-11-11
> UTC". If I try to read the timezone information from the date object in
> the ways possible for POSIX, I will get NULL as return:
> 
>  > attr(d, "tzone")
> NULL
> 
> Also unclassing the object does not reveal any information about the
> timezone, unlike for POSIX objects
>  > unclass(d)
> [1] 20038
> 
> In contrast, getting the timezone information with base::format will
> yield the timezone information
>  > base::format(d, format="%Z")
> [1] "UTC"
> 
> As for my current understanding, setting the tz Argument in as.Date will
> only have an effect if the input is a date-time such as POSIX and else
> it has no effect and it is not possible to set a timezone for an Date
> object. But is this the case if there is some timezone information
> present when using base::format or in the display in the RStudio
> environment? Is there any way to add timezone information to an Date
> object (other than UTC) and keeping it a Date object? And if not how is
> the Date object internally structured, so that it will return "UTC" when
> using base::format or in the RStudio environment? Is this due to some
> default behavior of R?
> 
> Best regards,
> 
> Luca
> 
> 
> My Session Info:
> R version 4.3.2 (2023-10-31 ucrt)
> Platform: x86_64-w64-mingw32/x64 (64-bit)
> Running under: Windows 11 x64 (build 22631)
> 
> Matrix products: default
> 
> 
> locale:
> [1] LC_COLLATE=German_Germany.utf8 LC_CTYPE=German_Germany.utf8
> LC_MONETARY=German_Germany.utf8
> [4] LC_NUMERIC=C                    LC_TIME=German_Germany.utf8
> 
> time zone: Europe/Berlin
> tzcode source: internal
>