Hi David, Thank you so much for your reply - the quick answer is that I inherited the R code I am working with from someone else so I am trying to use the same functions they have used. In hindsight, this did not make my life any easier - on the contrary. Of course, little did I know that I would find a bug in as.date() for the year 2000 and that I would not be able to apply strptime() to objects produced by as.date(). In the future, if given the option, I will stick with the as.Date() function you suggested.
Kind regards, Isabella -----Original Message----- From: David Winsemius [mailto:dwinsem...@comcast.net] Sent: November 10, 2009 8:58 PM To: Isabella Ghement Cc: Berwin A Turlach; r-help@r-project.org Subject: Re: [R] Unexpected behaviour for as.date() On Nov 10, 2009, at 11:11 PM, Isabella Ghement wrote: > 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")$year I do not have much, correction, make that no experience with the data package. I am wondering why you do not use the more "mainstream" function, as.Date: > d <- as.Date("02-MAY-07",format="%d-%b-%y") > d [1] "2007-05-02" It returns a Date formatted object that is the number of days from the origin, "1970-01-01". R generally "prefers" dates in the YYYY-MM-DD format, but allows conversion. ?Date Differences and addition are supported: > d - 1:10 [1] "2007-05-01" "2007-04-30" "2007-04-29" "2007-04-28" "2007-04-27" "2007-04-26" "2007-04-25" [8] "2007-04-24" "2007-04-23" "2007-04-22" > d + 1:10 [1] "2007-05-03" "2007-05-04" "2007-05-05" "2007-05-06" "2007-05-07" "2007-05-08" "2007-05-09" [8] "2007-05-10" "2007-05-11" "2007-05-12" > Sys.Date() - d Time difference of 923 days > > > d <- as.date(sub("-07", "-2007", "02-MAY-07"),order="dmy") > strptime(d, "%d%b%y")$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:ber...@maths.uwa.edu.au] > Sent: November 10, 2009 7:13 PM > To: Isabella Ghement > Cc: r-help@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" <isabe...@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 > > ========================== Full address ============================ > Berwin A Turlach Tel.: +61 (8) 6488 3338 (secr) > School of Maths and Stats (M019) +61 (8) 6488 3383 (self) > The University of Western Australia FAX : +61 (8) 6488 1028 > 35 Stirling Highway > Crawley WA 6009 e-mail: ber...@maths.uwa.edu.au > Australia http://www.maths.uwa.edu.au/~berwin > > ______________________________________________ > R-help@r-project.org mailing list > 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. David Winsemius, MD Heritage Laboratories West Hartford, CT ______________________________________________ R-help@r-project.org mailing list 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.
