[R] order() with randomised order in ties?

[Rainer M Krug]

Sorry for replying to my own post, but I found a solution. Still, a
more elegant solution would be preferred.

On Thu, Jun 4, 2009 at 12:02 PM, Rainer M Krug <r.m.krug at gmail.com> wrote:
> Hi
>
> I want to use order() to get the order of a vector.
>
> But I would need a different behavior when ties occur: similar to the
> parameter  ties.method = "random" in the rank() function, I would need
> to randomise the ties. Is this possible?

The solution is to randomize the vector before submitting to order():

x <- rep(1:10, 2)

iS <- sample( length(x) )
o <- order( x[iS], na.last=NA, decreasing=TRUE)
o
 [1]  8 16 12 17  2  9  7 15 10 11  4 14  3  5 13 20  1  6 18 19
x[iS][o]
 [1] 10 10  9  9  8  8  7  7  6  6  5  5  4  4  3  3  2  2  1  1

iS <- sample( length(x) )
o <- order( x[iS], na.last=NA, decreasing=TRUE)
o
 [1] 14 19 13 20  2 18  3 10  1 15  4  9 11 12  6  7  8 16  5 17
> x[iS][o]
 [1] 10 10  9  9  8  8  7  7  6  6  5  5  4  4  3  3  2  2  1  1


Thanks

Rainer

> Example:
>
> x <- rep(1:10, 2)
> order(x)
>  [1]  1 11  2 12  3 13  4 14  5 15  6 16  7 17  8 18  9 19 10 20
> order(x)
>  [1]  1 11  2 12  3 13  4 14  5 15  6 16  7 17  8 18  9 19 10 20
>
> ## I would need different "order" for the ties, as below in rank() example:
>
> rank(x, ties.method="random")
>  [1]  1  4  6  7 10 12 13 15 18 19  2  3  5  8  9 11 14 16 17 20
>> rank(x, ties.method="random")
>  [1]  2  4  5  7  9 12 14 15 18 19  1  3  6  8 10 11 13 16 17 20
>
>
> Thanks
>
> Rainer
>
> --
> Rainer M. Krug, Centre of Excellence for Invasion Biology,
> Stellenbosch University, South Africa
>



-- 
Rainer M. Krug, Centre of Excellence for Invasion Biology,
Stellenbosch University, South Africa