Confusion with Converting Factors to Dates using as.date
Thank you very much, Peter. As is often the case, R gave me exactly what I asked it to give me, but not what I wanted it to give me. :) Cheers, Josip Research Associate Human Security Report Project School for International Studies Simon Fraser University Suite 7200--515 W. Hastings St. Vancouver, BC V6B 5K3 Canada ----- Original Message ----- From: "Peter Dalgaard" <p.dalgaard at biostat.ku.dk> To: "Josip Dasovic" <j_dasovic at sfu.ca> Cc: r-help at r-project.org Sent: Wednesday, December 10, 2008 1:16:48 PM GMT -08:00 US/Canada Pacific Subject: Re: [R] Confusion with Converting Factors to Dates using as.date
Josip Dasovic wrote:
Dear R-Helpers: I'm having a problem getting dates into the correct format. I have a data frame, which is based on a .csv file that I imported into R via read.table. R has converted my date variables to factors; when I use the as.Date command, most of the values are converted "correctly" (and by this I guess I mean converted "as I wish them to be") but some have not been. Here's what I have: str(pk.df) 'data.frame': 206 obs. of 134 variables: $ uniqid : int 010 015 120 130 210 245 320 330 415 ... $ st_date : Factor w/ 154 levels "01/01/48","01/01/51",..: 46 27 NA 12 118 NA 63 127 NA NA ... ... I then convert them to a date class using st_date.new<-as.Date(st_date, "%m/%d/%y") This _seems_ to work... str(st_date.new) Class 'Date' num [1:206] 8150 8466 NA 33982 10149 ... But notice the 4th observation; I would like it to be 1963, not 2063. st_date.new[1:10] [1] "1992-04-25" "1993-03-07" NA "2063-01-15" "1997-10-15" [6] NA "1991-05-31" "1994-11-20" NA NA st_date[1:10] [1] 04/25/92 03/07/93 <NA> 01/15/63 10/15/97 <NA> 05/31/91 [8] 11/20/94 <NA> <NA> 154 Levels: 01/01/48 01/01/51 01/01/52 01/01/59 01/01/63 ... 12/31/96 I thought that the problem might be that I was converting a factor, so I first converted the variable to a character type (although I understand that this is done automatically) and then to date class, but I still had the same problem. Does anybody know how I can solve this and why I am getting this behavior? One more tidbit: the earliest date for which the date conversion is "correct" is 1969-04-15, while the most recent date for which the century is "incorrect" is 1967-11-05.
Well, to quote ?strptime:
'%y' Year without century (00-99). If you use this on input, which
century you get is system-specific. So don't! Often values
up to 68 (or 69) are prefixed by 20 and 69 (or 70) to 99 by
19.
O__ ---- Peter Dalgaard ?ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907