static double doubleAverage(int... a) {
  double sum = 0;
  for i over a:
    sum += a[i];
  ret doubleRatio(sum, l(a));
}

static double doubleAverage(double... l) {
  ret doubleRatio(doubleSum(l), l(l));
}

static double doubleAverage(Iterable<Double> l) {
  double sum = 0;
  long n = 0;
  fOr (Double i : l)
    if (i != null) { sum += i; ++n; }
  ret doubleRatio(sum, n);
}