I couldn't get your suggested method to work:

  `==.foo` <- function(a,b) unclass(a)==unclass(b)
  `>.foo` <- function(a,b) unclass(a) < unclass(b)     # invert comparison
  is.na.foo <- function(a)is.na(unclass(a))

  sort(structure(sample(5),class="foo"))  #-> 1:5  -- not reversed

What am I missing?

           -s

On Thu, May 28, 2009 at 5:48 PM, Duncan Murdoch <murdoch@stats.uwo.ca>wrote:

> On 28/05/2009 5:34 PM, Steve Jaffe wrote:
>
>> Sounds simple but haven't been able to find it in docs: is it possible to
>> sort a vector using a user-defined comparison function? Seems it must be,
>> but "sort" doesn't seem to provide that option, nor does "order" sfaics
>>
>
> You put a class on the vector (e.g. using class(x) <- "myvector"), then
> define a conversion to numeric (e.g. xtfrm.myvector) or actual comparison
> methods (you'll need ==.myvector, >.myvector, and is.na.myvector).
>
> Duncan Murdoch
>
>
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