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

[Joshua Ulrich]

On Fri, Oct 4, 2013 at 8:02 PM, Imanuel Costigan <i.costigan at me.com> wrote:
> Thanks for the responses and quoting the timezone help file.
>
> I am assuming that in order to determine the wday element of POSIXlt, R does the necessary calculations in Julian time (via POSIXct). Based on this excerpt from ?DateTimeClasses, it looks like R is responsible for determining time zones post 2037 (the example I gave was in 2038). So it could be an R issue.
>
It's an issue with size of the largest number you can store in a
signed integer, which is not specific to R.

> .POSIXct(.Machine$integer.max, tz="UTC")
[1] "2038-01-19 03:14:07 UTC"

Dates larger than that cannot be represented by a signed integer.  It
could be worked around, but it's not trivial because R would have to
use something other than the tm C struct.  Luckily, there's a decade
or two before it starts to become a pressing issue. :)

>>      ‘"POSIXct"’ objects may also have an attribute ‘"tzone"’, a
>>      character vector of length one.  If set to a non-empty value, it
>>      will determine how the object is converted to class ‘"POSIXlt"’
>>      and in particular how it is printed.  This is usually desirable,
>>      but if you want to specify an object in a particular timezone but
>>      to be printed in the current timezone you may want to remove the
>>      ‘"tzone"’ attribute (e.g. by ‘c(x)’).
>>
>>      Unfortunately, the conversion is complicated by the operation of
>>      time zones and leap seconds (24 days have been 86401 seconds long
>>      so far: the times of the extra seconds are in the object
>>      ‘.leap.seconds’).  **The details of this are entrusted to the OS
>>      services where possible.  This always covers the period 1970-2037,
>>      and on most machines back to 1902 (when time zones were in their
>>      infancy).  Outside the platform limits we use our own C code.
>
>
> On 05/10/2013, at 12:59 AM, Scott Kostyshak <skostysh at princeton.edu> wrote:
>
>> On Fri, Oct 4, 2013 at 6:11 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:
>>
>> Yes. Quote from Duncan:
>>
>>    ... the server is currently down. The volunteer who runs the server is
>>    currently away from his office, so I expect it won't get fixed until he
>>    gets back in a few days.
>>
>> https://stat.ethz.ch/pipermail/r-help/2013-October/360958.html
>>
>> Scott
>>
>>>
>>> ```
>>> 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
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>> --
>> Scott Kostyshak
>> Economics PhD Candidate
>> Princeton University
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel