[R] difftime() out by 1 hour

[PIKAL Petr]

Hi

The same with me on Windows
Most probably an issue of daylight savings time setting.

Sys.timezone()
[1] "CET"

Regards
Petr


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Pascal Oettli
> Sent: Friday, February 01, 2013 9:18 AM
> To: Boots
> Cc: R Help
> Subject: Re: [R] difftime() out by 1 hour
> 
> Hello,
> 
> Here is the result I get using your script:
> 
>  > sessionInfo()
> R version 2.15.2 (2012-10-26)
> Platform: x86_64-suse-linux-gnu (64-bit)
> 
> 
> [1] "2012-03-31 21:00:00" "2012-04-01 00:00:00" "2012-04-01 03:00:00"
> [4] "2012-04-01 06:00:00"
> Time differences in hours
> [1] 3 3 3
> attr(,"tzone")
> [1] ""
> [1] "2012-10-06 21:00:00" "2012-10-07 00:00:00" "2012-10-07 03:00:00"
> [4] "2012-10-07 06:00:00"
> Time differences in hours
> [1] 3 3 3
> attr(,"tzone")
> [1] ""
> 
> Regards,
> Pascal
> 
> 
> Le 01/02/2013 16:27, Boots a écrit :
> > I have a problem with results  from difftime being 1 hour different
> than expected. 2 examples are given below:
> >
> > datetime <- matrix(data=rbind(c("2012-03-31 21:00:00", "2012-04-01
> 00:00:00", "2012-04-01 03:00:00", "2012-04-01 06:00:00"),
> >                     c("2012-10-06 21:00:00", "2012-10-07 00:00:00",
> > "2012-10-07 03:00:00", "2012-10-07 06:00:00")), ncol=4, nrow=2)
> >
> > for (row in 1:2) {
> >    x <- datetime[row,]
> >    x1=x[1:length(x)-1]
> >    x2=x[2:length(x)]
> >    xd=difftime(x2,x1)
> >    print (x)
> >    print (xd)
> > }
> >
> > [1] "2012-03-31 21:00:00" "2012-04-01 00:00:00" "2012-04-01 03:00:00"
> "2012-04-01 06:00:00"
> > Time differences in hours
> > [1] 3 4 3
> > attr(,"tzone")
> > [1] ""
> > [1] "2012-10-06 21:00:00" "2012-10-07 00:00:00" "2012-10-07 03:00:00"
> "2012-10-07 06:00:00"
> > Time differences in hours
> > [1] 3 2 3
> > attr(,"tzone")
> > [1] ""
> >
> > Accurate results would be 3 3 3 (hours) in both cases.
> > The problem occurs randomly, but only around midnight.
> > All the dates between "2012-04-01 06:00:00" and "2012-10-06 21:00:00"
> are fine.
> >
> > I have seen postings about problems with "POSIXlt" and "POSIXct"
> > accuracy because of truncation rather than rounding of floating point
> representations.
> > The response was that it was expected behaviour.
> >
> > So my question is this expected behaviour, have I used difftime
> > incorrectly, and if not, is there a set of date/time functions and
> classes that use integer representation to give more accurate results?
> I am new to R and I may well be using the wrong set of functions.
> > Garry
> >
> > 	[[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.
> >
> 
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> guide.html
> and provide commented, minimal, self-contained, reproducible code.