entropyvctr = function(vctr) {
  total  = sum(vctr)
  totalh = Reduce(function(acc, element) {
    prb = element / total
    h   = if(prb == 0) 0 else prb*log2(prb)
    return (acc - h)
  }, vctr, 0)
  return (totalh)
}

entropy = function(assign, truth) {
  clusterlvls = levels(assign)
  clusterclss = table(assign, truth)

  n = nrow(clusterclss)
  entropywght = array(dim = c(n,2))
  pop = 0

  for (i in 1:n) {
    clustersz = sum(clusterclss[i,])
    pop = pop + clustersz
    entropywght[i,] = c(entropyvctr(clusterclss[i,]), clustersz)
  }

  perc = 0
  if (clusterlvls[1] == "0") {
    outliers = sum(clusterclss[1,])
    perc = outliers / pop
    pop = pop - outliers
    entropywght[1,] = c(0,0)
  }

  totalh = 0
  if (pop > 0) {
    for (i in 1:n) {
      totalh = totalh + entropywght[i,1] * entropywght[i,2] / pop
    }
  }

  return(c(totalh, perc))
}