Some statistics functions

Statistics.cs

using System;
using System.Collections.Generic;
using System.Numerics;

namespace Math.Statistics
{
	public static class Statistics
	{
		public static long Mean(this IEnumerable<long> data)
		{
			if (data == null) throw new ArgumentNullException("data");

			BigInteger sum = 0;
			int itemCount = 0;
			foreach (var value in data)
			{
				sum += value;
				itemCount ++;
			}
			if (itemCount == 0) throw new ArgumentException("data");

			return (long)(sum / itemCount);
		}

		public static double StdDev(this IEnumerable<long> data)
		{
			if (data == null) throw new ArgumentNullException("data");

			BigInteger σx = 0, σx2 = 0;
			int n = 0;
			foreach (var value in data)
			{
				σx += value;
				σx2 += (BigInteger)value * value;
				n++;
			}
			if (n == 0) throw new ArgumentException("data");

			BigInteger σ2 = σx * σx;
			return System.Math.Sqrt((double)((n * σx2) - σ2) / ((n - 1) * n));
		}
	}
}