StandardDeviation returns NaN for some identical double values on iOS

[giulitu95]

Hi!
I've encountered an issue when using this package in a Flutter app compiled for iOS. When trying to compute the standard deviation of a list of double values where all elements are the same, the result is NaN instead of the expected 0.0.

Here are a couple of example arrays that produce the issue:

[94.97, 94.97, 94.97, 94.97, 94.97, 94.97, 94.97]
[53.97, 53.97, 53.97, 53.97, 53.97, 53.97, 53.97]

Since all values are equal, the expected standard deviation should be 0.0.

Environment:

Flutter version: 3.29.2
Dart version: 3.7.2
statistics package version: 1.1.3
iOS target: 17.6.1

Minimal example

import 'package:statistics/statistics.dart';

void main() {
  final data1 = [94.97, 94.97, 94.97, 94.97, 94.97, 94.97, 94.97];
  final data2 = [53.97, 53.97, 53.97, 53.97, 53.97, 53.97, 53.97];

  final stdDev1 = data1.standardDeviation;
  final stdDev2 = data2.standardDeviation;

  print('Standard Deviation of data1: $stdDev1');
  print('Standard Deviation of data2: $stdDev2');
}

Expected Output

Standard Deviation of data1: 0.0
Standard Deviation of data2: 0.0

Actual Output

Standard Deviation of data1: NaN
Standard Deviation of data2: NaN

[gmpassos]

I'm adding your example as test, and the result on Dart VM, due floating point imprecision, is 1.4210854715202004e-14 (near zero).

    test('standardDeviation = 0 (1)', () {
      final data1 = [94.97, 94.97, 94.97, 94.97, 94.97, 94.97, 94.97];
      var standardDeviation = data1.standardDeviation;
      final stdDev1 = standardDeviation;
      print('Standard Deviation of data1: $stdDev1');

      expect(standardDeviation, equals(0.0));
    });

I will make some adjustments for this case...

[gmpassos]

FYI:
PR: #13

[gmpassos]

@giulitu95
If possible try the fix:

dependency_overrides:
  statistics:
    git:
      url: https://github.com/gmpassos/statistics.git
      ref: statistics-bigint-decimal