Divide Extension for foreach Func Lambda LINQ null String Length

Average

The C# Average() method is an extension method. It computes the average value using only one statement. Often we combine it with other LINQ methods.

Average notes

This method provides a declarative way to compute the average value of a sequence in the C# language. We can use Average() with no argument, or pass in a lambda expression.

Example

First, add the "using System.Linq" directive to include the LINQ namespace. The Average() method implementation is stored in the System.Core.dll file.

Tip The Average() method looks like an instance method when called, but it is not. It is an extension method.

Info The program shows how to directly average the values in a double array collection.

Note Average is equivalent to adding up the total of all of the numbers, and then dividing that total by the number of elements.

using System;
using System.Linq;

// Use Average to compute average value.
double[] array = { 1, 2, 3, 5, 0 };
double average = array.Average();
Console.WriteLine("AVERAGE: {0}", average);
AVERAGE: 2.2

Overload, lambda

There are more overloads to Average(). We can select the values we want to average from another collection with a selector delegate. We can pass a lambda expression.

Here We use the Average() method parameter to specify a function that will select a value from an existing sequence.

Tip The lambda expression extracts the length of the strings and then averages those values.

using System;
using System.Linq;

// Use Average to compute average string length.
string[] array = { "dog", "cat", "perls" };
double average = array.Average(x => x.Length);
Console.WriteLine("AVERAGE: {0}", average);
AVERAGE: 3.66666666666667

Internals

How does Average() work? If you provide a selector parameter to Average, the method internally calls the Select() extension method first.

Then On that result, Average() checks the parameter for null, uses a foreach-loop, and divides the total value by the count.

Also The Average() extension method will throw an exception if it divides by zero.

Warning Because of all the overhead in this method, this implementation will be slower than a for-loop approach.

Summary

You can use Average() to compute the average value of a collection of numbers. And you can combine the Average() extension with a Func selector. This will internally Select() elements.