[Rd] Date method of as.POSIXct does not respect tz

[Martin Maechler]

>>>>> Kurt Hornik 
>>>>>     on Fri, 23 Sep 2022 09:57:49 +0200 writes:

>>>>> Martin Maechler writes:

    > Currently in R-devel,

    R> as.POSIXlt.Date
    > function (x, ...) 
    > {
    >    if (any((y <- unclass(x)) > .Machine$integer.max, na.rm = TRUE)) 
    >         as.POSIXlt(.POSIXct(y * 86400), tz = "UTC")
    >    else .Internal(Date2POSIXlt(x))
    > }

    R> as.POSIXct.Date
    > function (x, ...) 
    > .POSIXct(unclass(x) * 86400)

    > Adding tz to the latter is easy, and the former could do the if() part
    > also with a given tz without needing to change the .Internal?

Genau!  Even more elegantly than I first thought when I wrote
"post-processing":

The following even adds internal consistency inside as.POSIXlt.Date() :

as.POSIXlt.Date <- function(x, tz = "UTC", ...) {
    as.POSIXlt(if(any((y <- unclass(x)) > .Machine$integer.max, na.rm = TRUE))
                   .POSIXct(y * 86400)
               else
                   .Internal(Date2POSIXlt(x))
             , tz = tz)
}

because now, tz is even *formally* treated the same in both
cases (whereas previously it only appeared visually in one case).

So probably, another reason to go there.
Note that I also think we'd keep the    tz = "UTZ"
default argument, even when the
other  as.POSIX[cl]t() methods have 'tz = ""'



>>>>> Roland Fuß 
>>>>>     on Tue, 20 Sep 2022 09:25:52 +0200 writes:

    >>> Hello, May I follow up on this? Has it fallen through the
    >>> cracks or were there considerations against passing `tz`
    >>> to `.POSIXct`?

    >>> Regards,
    >>> Roland

    >> Hmm...  I don't remember  even though I had replied positively
    >> to your question in May 2018.

    >> PROS (for allowing 'tz') to be passed to
    >> ----   as.POSIXct.Date()  and hence ideally also to as.POSIXlt.Date() 

    >> 1) as.POSIXct() and as.POSIXlt()   all show with a 'tz' argument
    >> on the help page, and hence for consistency users should
    >> really expect  that 'tz = ".."'  also works in these two cases:

    >> Usage:

    >> as.POSIXct(x, tz = "", ...)
    >> as.POSIXlt(x, tz = "", ...)
     
    >> ## S3 method for class 'character'
    >> as.POSIXlt(x, tz = "", format,
    >> tryFormats = c("%Y-%m-%d %H:%M:%OS",
    >> "%Y/%m/%d %H:%M:%OS",
    >> "%Y-%m-%d %H:%M",
    >> "%Y/%m/%d %H:%M",
    >> "%Y-%m-%d",
    >> "%Y/%m/%d"),
    >> optional = FALSE, ...)
    >> ## Default S3 method:
    >> as.POSIXlt(x, tz = "",
    >> optional = FALSE, ...)
    >> ## S3 method for class 'numeric'
    >> as.POSIXlt(x, tz = "", origin, ...)


    >> 2) It is easy to be implemented for  as.POSIXct()   as you found
    >> already in 2018.


    >> CONS:
    >> -----

    >> 3) The 'Details:' section on the help page,
    >> end of 1st paragraph says

    >> Dates without times are treated as being at midnight UTC.

    >> So the current hardwired behavior is documented.

    >> 4a) For  as.POSIXlt.Date()  to allow passing 'tz' needs changes
    >> in the C code,  i.e., is considerable more work than for the as.POSIXct(),
    >> (or actually just post-processing in the R code, much less work)

    >> 4b) Only changing the behavior for as.POSIXct()  but not for as.POSIXlt()
    >> is also an inconsistency.


    >> My personal inclination would still be to do the change,
    >> by giving most weight to  '1)' above.

    >> What do other experienced R developers think ?

    >> Martin


    >>> Am 17.05.2018 um 19:55 schrieb Martin Maechler:
    >>>>>>>>> Roland Fuß on Wed, 16 May 2018 17:21:07 +0200
    >>>>>>>>> writes:
    >>>> > R 3.5.0 Is it intended that the Date method of
    >>>> as.POSIXct > does not respect the tz parameter? I suggest
    >>>> changing > as.POSIXct.Date
    >>>> 
    >>>> which is
    >>>> 
    >>>> function (x, ...) .POSIXct(unclass(x) * 86400)
    >>>> 
    >>>> > to this:
    >>>> 
    >>>> function (x, tz = "", ...)  .POSIXct(unclass(x) * 86400,
    >>>> tz = tz)
    >>>> 
    >>>> or rather just forward the '...', i.e., use
    >>>> 
    >>>> function (x, ...) .POSIXct(unclass(x) * 86400, ...)
    >>>> 
    >>>> ??
    >>>> 
    >>>> > Currently, the best workaround seems to be using the >
    >>>> character method if one doesn't want the default timezone
    >>>> > (which is often an annoying DST timezone).
    >>>> 
    >>>> > This came up on Stack Overflow: >
    >>>> https://stackoverflow.com/q/50373340/1412059
    >>>> 
    >>>> > --
    >>>> > Roland
    >>>> 
    >>>> Thank you Roland for your notice (and the help on SO).
    >>>> 
    >>>> Best, Martin

    >>> -- 
    >>> Dr. Roland Fuß

    >>> Thünen-Institut für Agrarklimaschutz/ Thünen Institute of
    >>> Climate-Smart Agriculture

    >>> Bundesallee 65 D-38116 Braunschweig, Germany

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    >>> roland.fuss using thuenen.de

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    >>> The Johann Heinrich von Thünen Institute, Federal Research
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