[R] Date Calculation

[Prof Brian Ripley]

You have formatted the dates, so you are trying to subtract character 
strings.

Convert to Date instead (although you can subtract POSIXlt dates).

On Thu, 17 Jun 2004, Ko-Kang Kevin Wang wrote:

> Hi,
> 
> I've been playing with:
> > joinDate <- format(strptime(as.vector(forum[,2]), "%d-%b-%y"),
> +                    "%d-%b-%Y")
> > today <- format(strptime(as.vector("14-Jun-04"), "%d-%b-%Y"),
> +                 "%d-%b-%Y")
> > joinDate
>  [1] "04-Feb-2004" "13-Feb-2004" "26-Feb-2004" "27-Feb-2004"
> "27-Feb-2004"
>  [6] "27-Feb-2004" "29-Feb-2004" "01-Mar-2004" "02-Mar-2004"
> "07-Mar-2004"
> [11] "08-Mar-2004" "17-Mar-2004" "20-Mar-2004" "22-Mar-2004"
> "22-Mar-2004"
> [16] "23-Mar-2004" "23-Mar-2004" "24-Mar-2004" "01-Apr-2004"
> "01-Apr-2004"
> [21] "01-Apr-2004" "01-Apr-2004" "02-Apr-2004" "06-Apr-2004"
> "09-Apr-2004"
> [26] "11-Apr-2004" "14-Apr-2004" "03-May-2004" "04-May-2004"
> "30-May-2004"
> [31] "01-Jun-2004" "10-Jun-2004" "14-Jun-2004" "17-Jun-2004"
> "17-Jun-2004"
> > today
> [1] "14-Jun-0004"
> > joinDate - today
> Error in joinDate - today : non-numeric argument to binary operator
> 
> But it didn't quite work.  What I'd like joinDate - today to return is
> the number of days to today, since joinDate.  I'm sure it has been asked
> before however a search on r-help didn't found me any relevant
> information *_*.
> 
> Cheers,
> 
> Kevin
> 
> --------------------------------------------
> Ko-Kang Kevin Wang, MSc(Hon)
> SLC Stats Workshops Co-ordinator
> The University of Auckland
> New Zealand
> 
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> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595