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

[Kurt Hornik]

>>>>> 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?

Best
-k

>>>>> 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

>> Tel.: ++49 531 596 2627 Fax: ++49 531 596 2699 Email:
>> roland.fuss using thuenen.de

>> Arbeitsgruppe "Emissionsberichterstattung"/ Working group
>> "Emission Inventories" Email:
>> emissionsinventare using thuenen.de

>> Das Johann Heinrich von Thünen-Institut,
>> Bundesforschungsinstitut für Ländliche Räume, Wald und
>> Fischerei – kurz: Thünen-Institut – besteht aus 15
>> Fachinstituten, die in den Bereichen Ökonomie, Ökologie
>> und Technologie forschen und die Politik beraten.

>> The Johann Heinrich von Thünen Institute, Federal Research
>> Institute for Rural Areas, Forestry and Fisheries – Thünen
>> Institute in brief – consists of 15 specialized institutes
>> that carry out research and provide policy advice in the
>> fields of economy, ecology and technology.

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