For a security feature in a Silverlight project I needed to compute the standard deviation of a series. Googling for it I quickly found a code sample, but it dates from the days before LINQ, which makes it 70 lines-long.
Thanks to LINQ, you can write a method that computes a standard deviation with only 3 lines. It works with Silverlight 2 (and 3) and with whatever .NET 3.5 application (WPF, ASP.NET, ...). Here’s my code:
using System;
using System.Data.Linq;public static class SecurityMaths
{
public static double StandardDeviation(this IEnumerable<double> data)
{
double average = data.Average();
var individualDeviations = data.Select(num => Math.Pow(num - average, 2.0));
return Math.Sqrt(individualDeviations.Average());
}
}
Note that I defined my method as an extension method, so that it can be used just like the Average LINQ method. Which means you can use it that way:
double[] numbers = new double[] { 2,4,4,4,5,5,7,9 };
double average = numbers.Average();
double standardDev = numbers.StandardDeviation();
What a clean code: it’s almost as obvious as the mathematical definition of the standard deviation. Thanks a ton, LINQ!
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