Standard Deviation Calculation in .NET To Simulate Excel STDEVPABy Robbe D. MorrisPrinter Friendly Version Robbe & Melisa Morris
Here's a quick code sample that demonstrates how to calculate standard deviation for an array of values in .NET ( C# / VB.NET ).  This method duplicates the same standard deviation ( STDEVPA ) function that exists in Excel.

Sample Code
```using System;

namespace ConsoleApplication2
{

class Class1
{

[STAThread]
static void Main(string[] args)
{

double[] test1 = new double[7];
double[] test2 = new double[8];

try
{

test1[0] = 9;
test1[1] = 9;
test1[2] = 9;
test1[3] = 9;
test1[4] = 9;
test1[5] = 9;
test1[6] = 9;

test2[0] = 3.3;
test2[1] = 5.6;
test2[2] = 7.2;
test2[3] = 5.6;
test2[4] = 9;
test2[5] = 2.1;
test2[6] = 8.8;
test2[7] = 2.1;

// test #1 should return zero because there is
// no variance between any of the data points.

Console.WriteLine(StandardDeviation(test1).ToString());

Console.WriteLine(StandardDeviation(test2).ToString());

}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
finally
{
Console.ReadLine();
}
}

private static double StandardDeviation(double[] data)
{

double ret = 0;
double DataAverage = 0;
double TotalVariance = 0;
int Max = 0;

try
{

Max = data.Length;

if (Max == 0) { return ret; }

DataAverage = Average(data);

for(int i=0;i<Max;i++)
{
TotalVariance += Math.Pow(data[i] - DataAverage,2);
}

ret = Math.Sqrt(SafeDivide(TotalVariance,Max));

}
catch (Exception) { throw; }
return ret;
}

private static double Average(double[] data)
{

double ret = 0;
double DataTotal = 0;

try
{

for(int i=0;i<data.Length;i++)
{
DataTotal += data[i];
}

return SafeDivide(DataTotal,data.Length);

}
catch (Exception) { throw; }
return ret;
}

private static double SafeDivide(double value1,double value2)
{

double ret = 0;

try
{

if ((value1 == 0) || ( value2 == 0)) { return ret; }

ret =  value1 / value2;

}
catch { }
return ret;
}

}
}

```
 Robbe has been a Microsoft MVP in C# since 2004.  He is also the co-founder of NullSkull.com which provides .NET articles, book reviews, software reviews, and software download and purchase advice.