Unexpected behaviour for as.date()

Hi Berwin,

Many thanks for your fast reply!  It's evening time in Vancouver,  
Canada but
it must be day time in Australia, so
good day to you.

Sorry about the confusion regarding the library name - I am using  
the "date"
library, as you pointed out.

I tried the solution you suggested and find that am having problems  
getting
R to extract the year
from an object created by as.date():

d <- as.date(sub("-00", "-2000", "02-MAY-00"),order="dmy")
strptime(d, "%d%b%y")$year

d <- as.date(sub("-07", "-2007", "02-MAY-07"),order="dmy")
strptime(d, "%d%b%y")$year

Try this as well, just in case:

d <- as.date("02-MAY-07",order="dmy")
strptime(d, "%d%b%y")$year

How does one extract (a meaningful) year from the object d above?

Kind regards,

Isabella

Isabella R. Ghement, Ph.D.
Ghement Statistical Consulting Company
-----Original Message-----
From: Berwin A Turlach [mailto:berwin at maths.uwa.edu.au]
Sent: November 10, 2009 7:13 PM
To: Isabella Ghement
Cc: r-help at r-project.org
Subject: Re: [R] Unexpected behaviour for as.date()


G'day Isabella,

On Tue, 10 Nov 2009 18:40:11 -0800
"Isabella Ghement" <isabella at ghement.ca> wrote:

I am trying to use the function as.date() from the "dates" package

As far as I can tell, there is no package called "dates", did you mean
the package "date"?

in R 2.10.0 to convert a character date to a Julian date, as follows:

as.date("02-MAY-01", order="mdy") # convert May 2, 2001 to a Julian
date

[1] 2May1

Are you sure that you are doing what your comments imply?  Try:

R> library(date)
R> as.date("02-MAY-01", order="mdy")
[1] 2May1
R> as.date("02-MAY-2001", order="mdy")
[1] 2May2001
R> as.numeric(as.date("02-MAY-01", order="mdy"))
[1] -21428
R> as.numeric(as.date("02-MAY-2001", order="mdy"))
[1] 15097

However, when trying to convert a character date from the year 2000
to a Julian date, I get an <NA> instead of the desired Julian date:

as.date("02-MAY-00", order="mdy") # convert May 2, 2000 to a Julian
date

[1] <NA>

Not quite sure why R is unable to handle this type of date (perhaps  
it
thinks it comes from the year 1900?!).

My guess it thinks it comes from the year 0.  Not sure why it cannot
handle such dates.  But then, as far as I know, there is actually some
discussion about whether the year 0 exist or whether we went straight
from 1BC to 1AD......

Is there a way to force R to convert character dates from the year
2000 into Julian dates?

Presumably you will need something like:

R> as.date(sub("-00", "-2000", "02-MAY-00"))
[1] 2May2000

HTH.

Cheers,

	Berwin

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