R help - Jun 2010 - Problem with as.POSIXlt$hour

Hello,

In one of my functions, I need to extract the hour from a date.
For example:
as.POSIXlt("2010-03-27 02:00:00")$hour gives 2 as expected.
It works for all the dates I've tested except the following one which is in
my list of dates:
as.POSIXlt("2010-03-28 02:00:00")$hour which gives 0.

I don't understand why it doesn't work with this particular date.

Any idea ?

Thanks in advance,
Ptit Bleu (with R 2.9.0 under Windows ).

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On 15.06.2010 13:45, PtitBleu wrote:
>
> Hello,
>
> In one of my functions, I need to extract the hour from a date.
> For example:
> as.POSIXlt("2010-03-27 02:00:00")$hour gives 2 as expected.
> It works for all the dates I've tested except the following one which
is in
> my list of dates:
> as.POSIXlt("2010-03-28 02:00:00")$hour which gives 0.
 >
> I don't understand why it doesn't work with this particular date.
>
> Any idea ?
>
> Thanks in advance,
> Ptit Bleu (with R 2.9.0 under Windows ).
>

Perhaps it has been fixed within the last > 12 months since R-2.9.0 has 
been released?

Please try a recent version of R.

Uwe Ligges

On Jun 15, 2010, at 7:45 AM, PtitBleu wrote:
>
> Hello,
>
> In one of my functions, I need to extract the hour from a date.
> For example:
> as.POSIXlt("2010-03-27 02:00:00")$hour gives 2 as expected.
> It works for all the dates I've tested except the following one  
> which is in
> my list of dates:
> as.POSIXlt("2010-03-28 02:00:00")$hour which gives 0.
>
> I don't understand why it doesn't work with this particular date.
It "works" for me with a result of 2, so I suspect it has something to
do with whether that hour even "exists" during the shift from  
"ordinary" time to daylight savings time in your LOCALE (which was not
offered but would be plausibly near GMT/UMT given the domain from  
which you are posting).
>
> Any idea ?
>
> Thanks in advance,
> Ptit Bleu (with R 2.9.0 under Windows ).   ...
... wrong info for this question, I suspect.

-- 
David Winsemius, MD
West Hartford, CT

Hello again,

You are right: it corresponds to the DST time transition in France (I think
you have guessed it was France from my "Frenglish" style - sorry about
it).

To get around this problem, I now use :
as.numeric(format(strptime("2010-03-28 02:00:00",
format="%Y-%m-%d
%H:%M:%S"), format="%H"))

Thanks again for your help.
Ptit Bleu.
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