
Yea I thought that would be the story behind it.  Thanks.

> Date: Sun, 17 Feb 2008 16:15:27 -0500
> From: ggrothendieck@gmail.com
> To: bozhou1981@hotmail.com
> Subject: Re: [Rd] Arithmetic bug? (found when use POSIXct) (PR#10776)
> CC: r-devel@stat.math.ethz.ch
> 
> OK.  Good point.
> 
> Note that that article was written 4 years ago
> when R was at version 1.9 and POSIXt did not fully support
> subseconds.  At that time, POSIXct could represent subseconds
> internally but it was not used as POSIXlt did not yet support it
> and that and the associated digits.sec option did not come until
> R version 2.3, released two years after the article was written.
> 
> Try setting the digits.secs option before you run the command
> like this:
> 
> > options(digits.secs = 3)
> > dp <- Sys.time()
> > dp-as.POSIXct(format(dp,tz="GMT"))
> Time difference of -5 hours
> 
> On Feb 17, 2008 3:50 PM,  <bozhou1981@hotmail.com> wrote:
> >
> > Hi Gabo,
> >
> > FAQ 7.31 does not apply to this. "numeric" in R is 64bit which is large eno=
> > ugh to handle this.
> >
> > I
> > figured out the cause is that Sys.time() gives millisecond value while
> > b<-as.POSIXct(format(a,tz=3D"GMT")) cuts off that part.=20
> >
> > Then of course a-b is not 5 hours!
> >
> > Do it again with "options(digits=3D22)" and you will see what actually happ=
> > ened there.
> >
> > The recommended code from R News is not aware the truth that POSIXlt can re=
> > present sub-second time.
> >
> > Cheers,
> >
> > B
> > _________________________________________________________________
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