R/adj.rand.index.R

In feiyoung/simutool: Common Tool Functions In Simulation

adj.rand.index <-
  function(group1, group2) {
    a <- length(table(group1))
    N <- length(group1)
    ctab <- matrix(,a, a)
    for (j in 1:a) {
      for (i in 1:a) {
        ctab[j,i] <- length(which(group2[which(group1==i)]==j))
      }
    }
    sumnij <- sum(choose(ctab, 2))
    sumai <- sum(choose(colSums(ctab), 2))
    sumbj <- sum(choose(rowSums(ctab), 2))
    Ntwo <- choose(N, 2)
    ari <- abs((sumnij - (sumai*sumbj)/Ntwo)/(0.5*(sumai+sumbj)-(sumai*sumbj)/Ntwo))
    return(ari)
  }