fnVarianceValue function
VarianceValue(values): variance (population, divided by N)
Implementation
dynamic fnVarianceValue(List<dynamic> values) {
if (values.isEmpty) return 0.0;
final nums = values.map(varToDouble).toList();
final mean = nums.reduce((a, b) => a + b) / nums.length;
final sq = nums.map((x) => (x - mean) * (x - mean));
return sq.reduce((a, b) => a + b) / nums.length;
}