R help - Feb 2010 - difftime result for days not an integer?

Anybody have an idea why I would get a non-integer value for the
number of days here?
> difftime('2004-08-05','2001-01-03',units='days')
Time difference of 1309.958 days


Would you just round off?

Best,
Jon

On Thu, Feb 11, 2010 at 8:40 PM, Jonathan <jonsleepy at gmail.com>
wrote:
> Anybody have an idea why I would get a non-integer value for the
> number of days here?
>
>>
difftime('2004-08-05','2001-01-03',units='days')
> Time difference of 1309.958 days
>
>
> Would you just round off?
It's one hour short of an integer number of days:
>
difftime('2004-08-05','2001-01-03',units='hours')/24
Time difference of 1309.958 hours
>
(1+difftime('2004-08-05','2001-01-03',units='hours'))/24
Time difference of 1310 hours

 why do you think that might be?

 here's another hint: a few years ago my birthday only lasted 23
hours. I never got that hour back.

Barry

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On Thu, 11 Feb 2010, Jonathan wrote:
> Anybody have an idea why I would get a non-integer value for the
> number of days here?
>
>>
difftime('2004-08-05','2001-01-03',units='days')
> Time difference of 1309.958 days
Because it's not a whole number of 24-hour periods, due to daylight saving
time: 0.958 is 23/24.
>
> Would you just round off?
>
Yes, or use as.Date() if you only want to consider whole days

R> as.Date('2004-08-05')-as.Date('2001-01-03')
Time difference of 1310 days

        -thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle