[Rd] Possible POSIXlt / wday glitch & bugs.r-project.org status

[Joshua Ulrich]

Quoting from ?timezone:

     Note that except on Windows, the operation of time zones is an OS
     service, and even on Windows a third-party database is used and
     can be updated (see the section on ‘Time zone names’).  Incorrect
     results will never be an R issue, so please ensure that you have
     the courtesy not to blame R for them.

Best,
--
Joshua Ulrich  |  about.me/joshuaulrich
FOSS Trading  |  www.fosstrading.com


On Fri, Oct 4, 2013 at 5:11 AM, Imanuel Costigan <i.costigan at me.com> wrote:
> Wanted to raise two questions:
>
> 1. Is bugs.r-project.org down? I haven't been able to reach it for two or three days:
>
> ```
> ping bugs.r-project.org
> PING rbugs.research.att.com (207.140.168.137): 56 data bytes
> Request timeout for icmp_seq 0
> Request timeout for icmp_seq 1
> Request timeout for icmp_seq 2
> Request timeout for icmp_seq 3
> Request timeout for icmp_seq 4
> Request timeout for icmp_seq 5
> Request timeout for icmp_seq 6
> ```
>
> 2. Is wday element of POSIXlt meant to be timezone invariant? You would expect the wday element to be invariant to the timezone of a date. That is, the same date/time instant of 5th October 2013 in both Australia/Sydney and UTC should be a Saturday (i.e. wday = 6). And indeed that is the case with 1 min past midnight on 5 October 2013:
>
> ```
> library(lubridate)
> d_utc <- ymd_hms(20131005000001, tz='UTC')
> d_local <- ymd_hms(20131005000001, tz='Australia/Sydney')
> as.POSIXlt(x=d_utc, tz=tz(d_utc))$wday # 6
> as.POSIXlt(x=d_local, tz=tz(d_local))$wday # 6
> ```
>
> But this isn't always the case. For example,
>
> ```
> d_utc <- ymd_hms(20381002000001, tz='UTC')
> d_local <- ymd_hms(20381002000001, tz='Australia/Sydney')
> as.POSIXlt(x=d_utc, tz=tz(d_utc))$wday # 6
> as.POSIXlt(x=d_local, tz=tz(d_local))$wday # 5
> ```
>
> Is this expected behaviour? I would have expected a properly encoded date/time of 2 Oct 2038 to be a Saturday irrespective of its time zone.
>
> Obligatory system dump:
>
> ```
>> sessionInfo()
> R version 3.0.1 (2013-05-16)
> Platform: x86_64-apple-darwin12.4.0 (64-bit)
>
> locale:
> [1] en_AU.UTF-8/en_AU.UTF-8/en_AU.UTF-8/C/en_AU.UTF-8/en_AU.UTF-8
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] lubridate_1.3.0 testthat_0.7.1  devtools_1.3
>
> loaded via a namespace (and not attached):
>  [1] colorspace_1.2-4   dichromat_2.0-0    digest_0.6.3       evaluate_0.5.1
>  [5] ggplot2_0.9.3.1    grid_3.0.1         gtable_0.1.2       httr_0.2
>  [9] labeling_0.2       MASS_7.3-29        memoise_0.1        munsell_0.4.2
> [13] parallel_3.0.1     plyr_1.8           proto_0.3-10       RColorBrewer_1.0-5
> [17] RCurl_1.95-4.1     reshape2_1.2.2     scales_0.2.3       stringr_0.6.2
> [21] tools_3.0.1        whisker_0.3-2
>
> ```
>
> Using R compiled by homebrew [1]. But also experiencing the same bug using R installed on Windows 7 from the CRAN binaries.
>
> For those interested, I've also noted this on the `lubridate` Github issues page [2], even though this doesn't appear to be a lubridate issue.
>
> Thanks for any help.
>
> [1] http://brew.sh
> [2] https://github.com/hadley/lubridate/issues/209
>
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