function meanStdDev()

in src/toMidi.ts [137:154]

• 16 lines of code
• 1 McCabe index (conditional complexity)

function meanStdDev(array: number[][]): [number, number] {
  const [sum, sumSquared, count] = array.reduce(
    (prev, row) => {
      // Calculate N * E[x], N * E[x^2] and N
      const [rowSum, rowSumsSquared, rowCount] = row.reduce(
        (p, value) => [p[0] + value, p[1] + value * value, p[2] + 1],
        [0, 0, 0],
      );
      return [prev[0] + rowSum, prev[1] + rowSumsSquared, prev[2] + rowCount];
    },
    [0, 0, 0],
  );
  // E[x]
  const mean = sum / count;
  // sqrt( (1 / (N - 1)) * (E[x^2] - E[x]^2 / N))
  const std = Math.sqrt((1 / (count - 1)) * (sumSquared - (sum * sum) / count));
  return [mean, std];
}