[R] RE: problem with Dates

[Thomas Lumley]

On Fri, 18 Mar 2005, Benjamin Esterni wrote:

> It seems that you have load the "survival" package
> date.mdy is a function from this one.
> In this function the "origin" of the time is the first day of 1970
> in the base package the origin is the first day of 1960
> it's very curious...

Well, it would be very curious if they defined the same class, but the 
base package defines "Date" and the survival package defines "date". 
There's no reason why they should use the same origin, but it will cause 
problems if you mix them up.

 	-thomas

> Benjamin Esterni
> France
>
> From: "Vegard Andersen" <vegard.andersen at ism.uit.no>
> Subject: [R] Date conversion problem using "as.Date"
> To: "r-help at lists.r-project.org" <r-help at stat.math.ethz.ch>
> Message-ID: <opsntv38wtk0a1dr at petter-smart>
> Content-Type: text/plain; format=flowed; delsp=yes;
> charset=iso-8859-15
>
> Hello!
>
> My problem is that the Julian date "behind" my dates seems to be wrong. I
> will examplify my problem.
>
> t1 <- "1998-11-20"
> t2 <- as.Date(t1)
> # Here t2 is correctly "1998-11-20", but
> date.mdy(t2)
> $month
> [1] 11
> $day
> [1] 19
> $year
> [1] 1988
>
> And indeed, if I write: fix(t2) then I get : structure(10550, class =
> "Date"). So the Julian date is 10550, which is "1988-11-19", not the
> correct "1998-11-20"
>
> If I instead of "as.Date" use "as.date", then things work ok. But I have
> not found out how to instruct "as.date" to handle dates from the 21st
> century.
>
>
> I hope that someone can help me, thanks in advance!
>
> -- 
> Best regards,
> Vegard Andersen
> Institute of Community Medicine
> University of Tromso
> Tromso, Norway
> 	[[alternative HTML version deleted]]
>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle