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" <[EMAIL PROTECTED]>
To: "Josip Dasovic" <[EMAIL PROTECTED]>
Cc: r-help@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 Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
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