[Rd] The presence/absence of `zone` in POSIXlt depending on time zone as a cause of possible inconsistences?

[IAGO GINÉ VÁZQUEZ]

​Hi again,

I take advantage of my previous mail to ask you a question for which I was looking  for an answer when detected the behaviour I previously told. In the help of DataTimeClasses one can read:
"POSIXlt" objects will often have an attribute "tzone", a character vector of length 3 giving the time zone name from the TZ environment variable and the names of the base time zone and the alternate (daylight-saving) time zone. Sometimes this may just be of length one, giving the time zone name.
Then, I asked myself if the element `zone` of POSIXlt could be different of the attribute `tzone`. But I do not get that. I am not sure of understanding what the "time zone name from the TZ environment variable" is if not what I set through `Sys.setenv(TZ = "")`. But the next example does not behave as I would expect:

> Sys.setenv(TZ = "EDT")
> x <- as.POSIXlt(Sys.time(), "CET")

> x[1,"zone"]
[1] "CEST"

> attributes(x) $names  [1] "sec"    "min"    "hour"   "mday"   "mon"    "year"   "wday"   "yday"   "isdst"  "zone"   "gmtoff" $class [1] "POSIXlt" "POSIXt" $tzone [1] "CET"  "CET"  "CEST"

So `x[1,"zone"]` is what I expect, but I would expect `attributes(x)$tzone` would be related to `TZ = "EDT"`, and not to `tz = "CET"`. So, what am I understanding wrongly?

Thank you!
Stay safe,


Iago

________________________________
De: R-devel <r-devel-bounces using r-project.org> de part de IAGO GINÉ VÁZQUEZ <i.gine using pssjd.org>
Enviat el: divendres, 23 d’octubre de 2020 19:03
Per a: r-devel using r-project.org <r-devel using r-project.org>
Tema: [Rd] The presence/absence of `zone` in POSIXlt depending on time zone as a cause of possible inconsistences?

Dear all,

I have just detected what seems a minor inconsistence with data types. If one unlists a POSIXlt time with GMT zone gets a numeric vector, since the POSIXlt list has no `zone` element, while if one unlists a POSIXlt time with a non GMT zone (also non specifying tz if the Sys.timezone is not GMT) gets a character vector due to including the `zone` element.

> x <- as.POSIXlt(Sys.time(), "GMT")
> (y <- unlist(x))
      sec       min      hour      mday       mon      year      wday      yday     isdst
 54.99715  26.00000  16.00000  23.00000   9.00000 120.00000   5.00000 296.00000   0.00000
> str(y)
 Named num [1:9] 55 26 16 23 9 ...
 - attr(*, "names")= chr [1:9] "sec" "min" "hour" "mday" ...

> x <- as.POSIXlt(Sys.time(), "CET")
> (y <- unlist(x))
               sec                min               hour               mday                mon               year               wday               yday
"19.5111262798309"               "27"               "18"               "23"                "9"              "120"                "5"              "296"
             isdst               zone             gmtoff
               "1"             "CEST"             "7200"
> str(y)
 Named chr [1:11] "19.5111262798309" "27" "18" "23" "9" "120" "5" "296" "1" "CEST" "7200"
 - attr(*, "names")= chr [1:11] "sec" "min" "hour" "mday" ...

Is it expected? Why do not include always `zone` as an element of POSIXlt? Should POSIXlt objects be unlisted in a different way?
Thank you!
Best regards,

Iago

PS: I was using R 4.0.3. I don't know if this behaviour already changed in R-devel. Excuse me in that case.


        [[alternative HTML version deleted]]

______________________________________________
R-devel using r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

	[[alternative HTML version deleted]]