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