Median.cs

//http://msdn.microsoft.com/ja-jp/library/cc981895.aspx

public static class Extensions
{
    public static double Median(this IEnumerable<double> source)
    {
        var count = source.Count();
        if (count == 0) throw new InvalidOperationException("Cannot compute median for an empty set.");
        return source.OrderBy(x => x).Take((count / 2) + 1).Skip((count - 1) / 2).Average();
    }
}