quantile function

double? quantile(Iterable<num> iterable, double p)

Returns the p-quantile of the given iterable, where p is in 0, 1. Uses the R-7 method (linear interpolation of modes).

Implementation

double? quantile(Iterable<num> iterable, double p) {
  final values = iterable.toList()..sort();
  if (values.isEmpty) return null;
  if (p <= 0) return values.first.toDouble();
  if (p >= 1) return values.last.toDouble();

  final n = values.length;
  final index = (n - 1) * p;
  final lo = index.floor();
  final hi = index.ceil();
  final loValue = values[lo];

  if (lo == hi) return loValue.toDouble();

  return loValue + (values[hi] - loValue) * (index - lo);
}