Perhaps you are getting warning messages from difftime like this:

"Warning messages:
1: In structure(.Internal(as.POSIXct(x, tz)), class = c("POSIXt",
"POSIXct"),  :
  unable to identify current timezone 'V':
please set environment variable 'TZ'
2: In structure(.Internal(as.POSIXct(x, tz)), class = c("POSIXt",
"POSIXct"),  :
  unknwon timezone 'localtime'"

Try execute the code two times.

On Tue, Dec 9, 2008 at 3:33 PM, eric lee <ericlee100@gmail.com> wrote:

> Hi.  I'm trying to take the difference in days between two times.  Can
> you point out what's wrong, or suggest a different function?  When I
> try the following code,  The following code works fine:
>
> a <- strptime(1911100807,format="%Y%m%d%H",tz="GMT")
> b <- strptime(1911102718,format="%Y%m%d%H",tz="GMT")
> x <- difftime(b, a, units="days")
> x
>
>
> But when I change the year, the following code returns 'NA' for the
> time between a and b.  Thanks.
>
> a <- strptime(1999100807,format="%Y%m%d%H",tz="GMT")
> b <- strptime(1999102718,format="%Y%m%d%H",tz="GMT")
> x <- difftime(b, a, units="days")
> x
>
> ______________________________________________
> R-help@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.
>



-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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