Unexpected behaviour for as.date()

G'day Isabella,

On Tue, 10 Nov 2009 18:40:11 -0800

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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