[R] Finding (swapped) repetitions of numbers pairs across two columns

[Marc Schwartz]

On Dec 27, 2012, at 2:30 PM, Emmanuel Levy <emmanuel.levy at gmail.com> wrote:

> Hi,
> 
> I've had this problem for a while and tackled it is a quite dirty way
> so I'm wondering is a better solution exists:
> 
> If we have two vectors:
> 
> v1 = c(0,1,2,3,4)
> v2 = c(5,3,2,1,0)
> 
> How to remove one instance of the "3,1" / "1,3" double?
> 
> At the moment I'm using the following solution, which is quite horrible:
> 
> v1 = c(0,1,2,3,4)
> v2 = c(5,3,2,1,0)
> ft <- cbind(v1, v2)
> direction = apply( ft, 1, function(x) return(x[1]>x[2]))
> ft.tmp = ft
> ft[which(direction),1] = ft.tmp[which(direction),2]
> ft[which(direction),2] = ft.tmp[which(direction),1]
> uniques     = apply( ft, 1, function(x) paste(x, collapse="%") )
> uniques     = unique(uniques)
> ft.unique   = matrix(unlist(strsplit(uniques,"%")), ncol=2, byrow=TRUE)
> 
> 
> Any better solution would be very welcome!
> 
> All the best,
> 
> Emmanuel


Try this:

> unique(t(apply(cbind(v1, v2), 1, sort)))
     [,1] [,2]
[1,]    0    5
[2,]    1    3
[3,]    2    2
[4,]    0    4


Basically, sort each row so that you don't have to worry about the permutations of values, then get the unique rows as a result.

Regards,

Marc Schwartz