Hi Ben and Josh,
No, I don't think that there is a bug. It's just due to my lack of knowledge
on Date class, I was simply amazed that it has the daylight saving time built
in at first. But on the second thought, it really should.
Thank you all for the explanations!
...Tao
From: Ben Bolker <bbol...@gmail.com>
To: "Shi, Tao" <shida...@yahoo.com>
Cc: "r-h...@stat.math.ethz.ch" <r-h...@stat.math.ethz.ch>
Sent: Saturday, October 30, 2010 7:22:04 AM
Subject: Re: [R] date calculation
On 10-10-30 02:02 AM, Shi, Tao wrote:
> Hi Ben,
>
> That must be the case! In fact if I do:
>
>> difftime(strptime("24NOV2004", format="%d%b%Y"),
>> strptime("13MAY2004",format="%d%b%Y"), units="days", tz="GMT")
> Time difference of 195 days
>
>
> which supports your claim.
>
> Can someone from the R development team confirm this?
>
> Thanks!
>
> ...Tao
>
>
It sounds like you think this is a bug. It's not (although it's
arguably not what you want). The general advice when using dates and
time in R is to use the *least* specific date format that will do what
you want, i.e. don't use a format that incorporates time zone
information (daylight savings time) information if you don't want to
deal with these complexities.
I would suggest the chron package:
library(chron)
diff(chron(dates.=c("24/11/2004","13/05/2004"),format="d/m/y"))
>
>
>
> ----- Original Message -----
>> From:Ben Bolker <bbol...@gmail.com>
>> To:r-h...@stat.math.ethz.ch
>> Cc:
>> Sent:Friday, October 29, 2010 7:54:53 PM
>> Subject:Re: [R] date calculation
>>
>>
>> Shi, Tao <shidaxia <at>
>> href="http://yahoo.com";>yahoo.com> writes:
>
>> Could someone
>> explain to me why the following result is not a integer?
>>
>>>
>> difftime(strptime("24NOV2004", format="%d%b%Y"), strptime("13MAY2004",
>>
>>> format="%d%b%Y"), units="days")
>> Time difference of 195.0417
>> days
>
> Presumably because this goes across a daylight-savings
>> time
> adjustment? 0.0417=1/24 days is 1 hour ...
>
> Ben
>> Bolker
>
> ______________________________________________
>
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>
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>>> 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.
>
>
>
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