Re: [R] Date Not Staying in Date Format

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Tue 31 Jan 2006 - 13:01:41 EST

Using this test data, say:

   dd <- Sys.Date() + 0:9
   fac <- gl(5,2)

Try this:

   do.call("c", tapply(dd, fac, max, simplify = FALSE))

or if a list result is ok then just

   tapply(dd, fac, max, simplify = FALSE)

Another possibility using the as.Date.numeric method in the zoo package is:

  library(zoo)
  as.Date(tapply(dd, fac, max))

For more info on the internal representation of "Date" class objects see the Help desk article in R News 4/1.

On 1/30/06, David Randel <davidr00@hotmail.com> wrote:
> I have a column in a data frame that has a class of "Date" and a mode of
> "numeric". When I:
>
> max(df$Date)
>
> My output stays in Date format, i.e. "2006-01-03".
>
> However, when I run the following statment:
>
> tapply(df$Date, df$SomeFactor, max)
>
> my output looks like this: 9129 9493 9861 10226 10591 10956 11320
> 11687 12052 12417
>
> The returned object is of mode "numeric" and class "array". Each array
> element is of mode "numeric" and class "numeric". I believe that this is
> the integer representation of my date. I can't seem to convert it back to a
> date.
>
> How do I get these to be intrepreted as a date instead of a number?
>
> Thanks,
> ~Dave R.
>
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R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Jan 31 13:09:03 2006

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