[R] A co-occurrence matrix

["Hüsing, Johannes"]

>       [,1] [,2] [,3] [,4] [,5]
>  [1,] 1    0    1    1    0
>  [2,] 0    1    0    0    0
>  [3,] 1    0    1    1    0
>  [4,] 1    0    1    1    0
>  [5,] 0    0    0    0    1
> 
> where all zeros mean that these objects are not 
> in same group, and vice versa.

This is a block diagonal matrix of 1s and 0s 
with rows and cols permuted.

A block diagonal matrix can be set up with:

blockdiag <- function (v) {
  n <- sum(v)
  onezero <- function(k) {
    c(rep(c(rep(1,k), rep(0,n-k)), k), rep(0,k))
  }
  array(unlist(sapply(v, onezero))[1:(n*n)], c(n,n))
}

John's answer just came in; it seems more elegant to me.

Greetings


Johannes