[R] retaining "POSIXct" formatting when using apply(muff, FUN=MAX) on POSIXct dataframe?

[jim holtman]

It all depends on what you are doing.  Take a look at 'apply'; it says:

If X is not an array but has a dimension attribute, apply attempts to
coerce it to an array via as.matrix if it is two-dimensional (e.g.,
data frames) or via as.array.

Now take a look at what happens when you convert your dataframe to a matrix:

> x <- as.matrix(mydf)
> str(x)
 chr [1:2, 1:10] "2008-01-08 23:29:25" "2008-01-08 23:29:25"
"2008-01-08 23:29:25" ...
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:10] "X1" "X2" "X3" "X4" ...
>

It is a character matrix.

On Jan 8, 2008 12:28 PM, Thomas Pujol <thomas.pujol at yahoo.com> wrote:
> How do I retain "POSIXct" formatting when using apply, with FUN=max?
>
>  #example:
>  mydata <- rep(Sys.time(), 10)
> mydf <- data.frame(matrix(data=mydata, nrow=2, ncol=length(mydata) ) )
> for(i in seq(mydf))class(mydf[[i]]) <- class(mydata)
> str(mydf)
> maxdates <- apply(mydf,2,max,na.rm=T)
> str(maxdates)
>
>  #Why is the formattign now "chr", and not "POSIXct"?
>  #Is there a good way to retin "POSIXct" formatting?
>
>
>
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-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?