[Rd] Non-deterministic POSIXlt tzone in Europe/London around UTC 0

[Ben Bolker]

   It seems not so much non-deterministic, as different on the first vs. 
following invocations ...


$ cat tz.R
Sys.setenv(TZ="Europe/London")
for (i in 1:10) {
    print(attr(as.POSIXlt(as.numeric(1:10)), 'tzone'))

$ Rscript  tz.R
[1] "Europe/London" "GMT"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"

$ Rscript  tz.R
[1] "Europe/London" "GMT"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"

$ Rscript  tz.R
[1] "Europe/London" "GMT"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"
[1] "Europe/London" "BST"           "BST"


On 1/14/26 17:47, Michael Chirico via R-devel wrote:
> As a test case I have code running 'as.POSIXlt(1:10)', which can
> unfortunately produce non-deterministic results:
> 
> TZ=Europe/London R
> attr(as.POSIXlt(as.numeric(1:10)), 'tzone')
> # [1] "Europe/London" "GMT"           "BST"
> attr(as.POSIXlt(as.numeric(1:10)), 'tzone')
> # [1] "Europe/London" "BST"           "BST"
> 
> Is this intended behavior? I don't see this possibility described in
> any of ?DateTimeClasses, ?strptime, ?timezones, or ?as.POSIXlt. Some
> caching is mentioned around .sys.timezone, but the above snippets
> don't have any relationship that I can see.
> 
> Mike C
> 
> ______________________________________________
> R-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

-- 
Dr. Benjamin Bolker
Professor, Mathematics & Statistics and Biology, McMaster University
Associate chair (graduate), Mathematics & Statistics
Director, School of Computational Science and Engineering
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