[R] time zone issue - beginners question

[Gabor Grothendieck]

On Wed, Jul 6, 2011 at 10:37 AM, B Laura <gm.spam2011 at gmail.com> wrote:
> Hello all!
>
> As beginner I'm struggling for a while with time zones issue and can't find
> a suitable solution.
> I would be grateful for any help.
>
> Dataset imported from excel has a variable transplant.date which has been
> recorded with CET time zone.
>
>> subDataset$transplant.date
>  [1] "2000-01-01 CET" "2000-01-01 CET" "2000-01-02 CET" "2000-01-02 CET"
> "2000-01-02 CET" "2000-01-02 CET" "2000-01-04 CET" "2000-01-04 CET"
> "2000-01-04 CET" "2000-01-04 CET" "2000-01-04 CET" "2000-01-05 CET"
> "2000-01-05 CET"
> [14] "2000-01-05 CET" "2000-01-05 CET"
>
>
> However
>> Sys.time()
> [1] "2011-07-06 15:22:44 CEST"
>
> I need to calculate time difference in days but I'm still getting wrong
> calculations. Most likely is this time zone issue.
>
>
>> as.numeric(as.Date("2000-1-1")-as.Date(subDataset$transplant.date))
> [1] 1 1 0 0 0 0 -2 -2 -2 -2 -2 -3 -3 -3 -3
>
>
> Truncation doesn't help either
>
>>
> trunc(as.Date("2000-1-1"),"days")-trunc(as.Date(subDataset$transplant.date),"days")
> Time differences in days
>  [1]  1  1  0  0  0  0 -2 -2 -2 -2 -2 -3 -3 -3 -3
>
>

If you don't have times, which seems to be the situation here, use
"Date" class rather than "POSIXct".  Then you can't have time zone
issues in the first place.  See R News 4/1.

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