Is this a desirable change?
I would have expected sort to be equivalent to using order.
Thanks,
Stephen
Message
From: Duncan Murdoch [mailto:murdoch (AT) stats (DOT) uwo.ca]
Sent: Thursday, August 03, 2006 11:33 AM
To: Ponzio, Stephen [CIB-LAVA]
Cc: r-devel (AT) stat (DOT) math.ethz.ch; R-bugs (AT) biostat (DOT) ku.dk
Subject: Re: [Rd] sort changes datatype of operand (PR#9121)
8/3/2006 10:34 AM, stephen.ponzio (AT) citigroup (DOT) com wrote:
Full_Name: Stephen Ponzio
Version: 2.3.1
S: Windows
Submission from: (NULL) (199.67.138.42)
Given a vector of dates, sort returns a vector of numerics instead of dates.
This is different from the behavior in version 2.2, where dates were returned.
In this respect, sort is not equivalent to order.

>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

>class(dates[order(dates)])
[1] "Date"
>class(sort(dates))
[1] "numeric"
This is not a bug, it's documented behaviour in ?sort:
As from R 2.3.0, all attributes are removed from the return value
except names, which are sorted. (If 'partial' is specified even
the names are removed.) Note that this means that the returned
value has no class, except for factors and ordered factors (which
are treated specially and whose result is transformed back to the
original class).
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
You could put this into your own sort.Date function, but it won't be
called automatically: sort is not a generic.
sort.Date <- function(x) {
cl <- class(x)
structure(sort(x), class=cl)
}
Duncan Murdoch
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