[Rd] sort changes datatype of operand (PR#9121)

[Brahm, David]

On 8/3/2006 10:34 AM, <stephen.ponzio at citigroup.com> noted that,
starting with R-2.3.0, sort() fails to preserve date classes:

> dates <- seq(Sys.Date(), len=5, by="1 day")
> dates[order(dates)]
> [1] "2006-08-03" "2006-08-04" "2006-08-05" "2006-08-06" "2006-08-07"
> sort(dates)
> [1] 13363 13364 13365 13366 13367

and Duncan Murdoch <murdoch at stats.uwo.ca> replied:

> The problem is that some classes assume a particular ordering for
> values; sort can mess them up.  If you know that's not the case, you
> can protect the class yourself:
>   cl <- class(dates)
>   sorteddates <- sort(dates)
>   class(sorteddates) <- cl

I have to agree with Stephen (and Alex Dannenberg in another post)
that this change is unfortunate for date classes.  How do you
reproduce this old behavior (without assuming alphanumeric ordering):

> x <- matrix(1:12, 4,3)
> group <- Sys.Date() + c(0,1,0,1)
> rowsum(x, group)
           [,1] [,2] [,3]
2006-08-17    4   12   20
2006-08-18    6   14   22

Under R-2.3.1, the result is now:
      [,1] [,2] [,3]
13377    4   12   20
13378    6   14   22

Blech!

-- David Brahm (brahm at alum.mit.edu)