static double digitalVariation(int[] array) {

  int n = l(array);

  if (n == 0) ret 0; // ? - undefined

  if (n == 1) ret 0;

  var value = array[0];

  int deviations = 0;

  for (int i = 1; i < n; i++)

    if (array[i] != value)

      ++deviations;

  ret doubleRatio(deviations, n);

}

static <A> double digitalVariation(Iterable<A> l) {

  var it = iterator(l);

  if (!it.hasNext()) ret 0; // ? - undefined

  int n = 1;

  var value = it.next();

  int deviations = 0;

  while (it.hasNext()) {

    ++n;

    if (!eq(value, it.hasNext()))

      ++deviations;

  }

  ret doubleRatio(deviations, n);

}