[Rd] Proposal unary - operator for factors

[Prof Brian Ripley]

On Wed, 3 Feb 2010, Duncan Murdoch wrote:

> On 03/02/2010 7:20 PM, Hadley Wickham wrote:
>>>> Currently, for numeric a you can do either
>>>>   order(-a)
>>>> or
>>>>   order(a, decreasing=FALSE)
>>>> For nonnumeric types like POSIXct and factors only
>>>> the latter works.
>>>> 
>>>> Under my proposal your
>>>>   order(a, -b, c, d)
>>>> would be
>>>>   order(a, b, c, d, decreasing=c(FALSE,TRUE,FALSE,TRUE))
>>>> and it would work for any ordably class without modifications
>>>> to any classes.
>>> Why not use
>>>
>>>  order(a, -xtfrm(b), c, -xtfrm(d))
>> 
>> That's a good suggestion.  You could make it even easier to read with
>> desc <- function(x) -xtfrm(x)
>> 
>> order(a, desc(b), c, desc(d))
>> 
>> Could you remind me what xtfrm stands for?
>
> No, I don't think I ever worked it out. :-)

The same logic as strxfrm.

>
> Duncan Murdoch
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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