variance method

double variance()

Calculates variance of items.

Throws StateError if the iterable is empty.

Implementation

double variance() {
  if (isEmpty) {
    throw StateError('Iterable is empty');
  }
  // TODO: Optimize?
  final mean = this.mean();
  return map((e) {
    final v = e - mean;
    return v * v;
  }).mean();
}