# [R] pairwise combinatons of variables

Gabor Grothendieck ggrothendieck at gmail.com
Sat Mar 25 20:37:57 CET 2006

```See this recent post:

https://www.stat.math.ethz.ch/pipermail/r-help/2006-March/091066.html

On 3/25/06, Mark Hempelmann <neo27 at t-online.de> wrote:
> Dear WizaRds,
>
>        although this might be a trivial question to the community, I was unable to
>
> Suppose I have 4 variables and want to use all possible combinations:
> 1,2
> 1,3
> 1,4
> 2,3
> 2,4
> 3,4
> for a further kmeans partitioning.
>
> I tried permutations() of package e1071, but this is not what I need. Thank you
> for your help and support.
>
> mark.
> ---------------------------------------------------------------------
>
> Additionally: For anybody who is willing to offer some advise, here is my
> complete approach:
> library(e1071)
>
> mat <- matrix( c(6,7,8,2,3,4,12,14,14, 14,15,13,3,1,2,3,4,2,
> 15,3,10,5,11,7,13,6,1, 15,4,10,6,12,8,12,7,1), ncol=9, byrow=T )
> rownames(mat) <- paste("v", 1:4, sep="" )
>
> tmat <- t(mat)
> cluster         <- c(1, 2, 1, 3, 3, 3, 1, 2, 2)
> centroids       <- matrix( 0, ncol=3, nrow=4 )
> obj             <- vector(mode="list", length=3)
>
> for (j in 1:4){
>        for (i in 1:3){
>        where <- which(cluster==i) # which obj is in which class?
>        centroids[j,i] <- mean( tmat[ where,j ] )
>        obj[[i]] <- tmat[where,]
>        }
> }
> colnames(centroids) <- paste( c("Cluster"), 1:3)
> rownames(centroids) <- rownames(mat)
>
> centroids
> obj
>
> ##      now I want to do kmeans of all possible variable pairs, e.g. v1 and v3
> ##      automization in a second step later
> wjk     <- kmeans(tmat[,c(1,3)], centers=centroids[c(1,3),], iter.max=10,
> algorithm="MacQueen")   ## obviously wrong
>
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