static double standardDeviation(int... a) {
  if (empty(a)) ret 0;
  double avg = doubleAverage(a), sum = 0;
  for i over a: sum += sqr(a[i]-avg);
  ret sqrt(sum/l(a));
}

static double standardDeviation(double... a) {
  if (empty(a)) ret 0;
  double avg = doubleAverage(a), sum = 0;
  for i over a: sum += sqr(a[i]-avg);
  ret sqrt(sum/l(a));
}

static double standardDeviation(Collection<Double> a) {
  if (empty(a)) ret 0;
  double avg = doubleAverage(a), sum = 0;
  for (double d : a) sum += sqr(d-avg);
  ret sqrt(sum/l(a));
}