From pdalgd at gmail.com  Wed Apr 17 23:16:22 2013
From: pdalgd at gmail.com (peter dalgaard)
Date: Wed, 17 Apr 2013 23:16:22 +0200
Subject: [Rd] POSIXt oddness at end of 1969
In-Reply-To: <E66794E69CFDE04D9A70842786030B931C2DA557@PA-MBX01.na.tibco.com>
References: <E66794E69CFDE04D9A70842786030B931C2DA557@PA-MBX01.na.tibco.com>
Message-ID: <E6496482-B5C1-416F-AE1D-DC61D36DC188@gmail.com>

Same thing happens on OS X. A bit of googling (did you know that Jimi Hendrix and the Band of Gypsies played at the Fillmore East on December 31, 1969?) reveals that the root issue is that mktime() returns -1 if the calendar time cannot be represented, which makes the case where the time _can_ be represented as -1 a bit tricky!

People have come up with heuristics to detect this case, but I wonder if it's worth it. Take a look at
http://stackoverflow.com/questions/14049047/unix-c-get-time-at-a-different-zone

There has to be a simpler way, though. 

-pd

On Apr 17, 2013, at 22:10 , William Dunlap wrote:

> A user here noticed the following difference between Linux and Windows versions
> of R-2.15.3 (and R-3.0.0, I think) when using times within a second of the end of 1969:
> 
> f <- function (sec = -1) 
> {
>    x1 <- as.POSIXct(c(2 * sec, sec, 0), origin = "1970-01-01",  tz = "UTC")
>    x2 <- as.POSIXlt(x1)
>    x3 <- as.POSIXct(x2, origin = "1970-01-01", tz = "UTC")
>    list(x1 = x1, x2 = x2, x3 = x3)
> }
> 
> On Windows I get:
>> f(-1)
>  $x1
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] "1969-12-31 23:59:59 UTC"
>  [3] "1970-01-01 00:00:00 UTC"
> 
>  $x2
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] "1969-12-31 23:59:59 UTC"
>  [3] "1970-01-01 00:00:00 UTC"
> 
>  $x3
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] "1969-12-31 23:59:59 UTC"
>  [3] "1970-01-01 00:00:00 UTC"
> 
> On Linux I get an NA in x3 for 1 second before 1970:
>> f(-1)
>  $x1
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] "1969-12-31 23:59:59 UTC"
>  [3] "1970-01-01 00:00:00 UTC"
> 
>  $x2
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] "1969-12-31 23:59:59 UTC"
>  [3] "1970-01-01 00:00:00 UTC"
> 
>  $x3
>  [1] "1969-12-31 23:59:58 UTC"
>  [2] NA
>  [3] "1970-01-01 00:00:00 UTC"
> 
> On Windows, sessionInfo() is
>  R version 2.15.3 (2013-03-01)
>  Platform: x86_64-w64-mingw32/x64 (64-bit)
> 
>  locale:
>  [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
>  [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
>  [5] LC_TIME=English_United States.1252    
> 
>  attached base packages:
>  [1] stats     graphics  grDevices utils     datasets  methods   base     
> 
> On Linux,  sessionInfo() is
>> sessionInfo()
>  R version 2.15.3 (2013-03-01)
>  Platform: x86_64-unknown-linux-gnu (64-bit)
> 
>  locale:
>   [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8
>   [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
>   [7] LC_PAPER=C                 LC_NAME=C                  LC_ADDRESS=C
>  [10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
> 
>  attached base packages:
>  [1] stats     graphics  grDevices utils     datasets  methods   base
> 
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com



[Rd] POSIXt oddness at end of 1969
peter dalgaard