R help - May 2008 - Strange behaviour of as.POSIXct

Hi:
 
I do not understand the returned value of NA in the following, which is a
simplified version of
my attempt to convert the start column of the data frame AirQual in the SwissAir
package.
 
as.POSIXct(paste('04.04.2004 0',0:3,sep=''),format='%d.%m.%Y
%H')
[1] "2004-04-04 00:00:00 EST" "2004-04-04 01:00:00 EST"
[3] NA                        "2004-04-04 03:00:00 EDT"
 
My sessionInfo() is
 
 sessionInfo()
R version 2.7.0 (2008-04-22)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods
[7] base
 
Thank you,
 
Norm

	[[alternative HTML version deleted]]

I don't suppose April 4 happens to be the date when "daylight savings 
time" began in 2004?

In which case 2:00 AM is a time that doesn't exist ("spring
forward" at 02:00)

-Don

At 5:48 PM -0400 5/26/08, Josephy, Norman wrote:
>Hi:
>
>I do not understand the returned value of NA in the following, which 
>is a simplified version of
>my attempt to convert the start column of the data frame AirQual in 
>the SwissAir package.
>
>as.POSIXct(paste('04.04.2004
0',0:3,sep=''),format='%d.%m.%Y %H')
>[1] "2004-04-04 00:00:00 EST" "2004-04-04 01:00:00 EST"
>[3] NA                        "2004-04-04 03:00:00 EDT"
>
>My sessionInfo() is
>
>  sessionInfo()
>R version 2.7.0 (2008-04-22)
>i386-pc-mingw32
>locale:
>LC_COLLATE=English_United States.1252;LC_CTYPE=English_United 
>States.1252;LC_MONETARY=English_United 
>States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>attached base packages:
>[1] stats     graphics  grDevices utils     datasets  methods
>[7] base
>
>Thank you,
>
>Norm
>
>	[[alternative HTML version deleted]]
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

-- 
---------------------------------
Don MacQueen
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
macq at llnl.gov

>From the help page for strptime
      Remember that in most timezones some times do not occur and some
      occur twice because of transitions to/from summer time.  What
      happens in those cases is OS-specific.

Now Switzerland will have times in CET and not in EST5EDT, and the DST 
transition times are different in different countries.  Add tz="CET"
to
your call (or "Europe/Zurich").

On Mon, 26 May 2008, Josephy, Norman wrote:
> Hi:
>
> I do not understand the returned value of NA in the following, which is 
> a simplified version of my attempt to convert the start column of the 
> data frame AirQual in the SwissAir package.
>
> as.POSIXct(paste('04.04.2004
0',0:3,sep=''),format='%d.%m.%Y %H')
> [1] "2004-04-04 00:00:00 EST" "2004-04-04 01:00:00 EST"
> [3] NA                        "2004-04-04 03:00:00 EDT"
>
> My sessionInfo() is
>
> sessionInfo()
> R version 2.7.0 (2008-04-22)
> i386-pc-mingw32
> locale:
> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods
> [7] base
>
> Thank you,
>
> Norm
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595