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Often times when dealing with large lists of numbers (or strings), we need to find the average value of the list. Maybe we are calculating a student's GPA, or trying find the average age of visitors to a website. In the 2.0 world, we had to create a loop (typically foreach), count all the values in the list, then divide by the number of items in the list. Now, thanks to LINQ, we can call a new extension – Average.

Microsoft Explanation:

Computes the average of a sequence of nullable Int32
values that is obtained by invoking a projection function on each element of the
input sequence.

In layman's terms, it calculates the average of a list of Int32 values, and returns the result as a double.

Using our scenario above, let's calculate the average age of visitors to a website, using the 2.0 method, and the new LINQ Average method.

Calculating Average Age of Visitors Using C# 2.0

// build a list and get the average value of the list
List<int> AgeList = new List<int>() { 25, 25, 26, 32, 27, 22, 42, 50, 23, 18, 51 };

// holds the sum of ages from the list
int AgeCounter = 0;

// loop through the list and get the sum of all ages
foreach (int age in AgeList)
    AgeCounter += age;

// get the average of all ages (Sum / Number of items in list)
double avg = AgeCounter / AgeList.Count;

// output the result
Console.WriteLine(string.Format("Average value of list: {0}", avg));

// Outputs:
// Average value of list: 31

 

Calculating Average Age of Visitors Using LINQ Average

// build a list and get the average value of the list
List<int> AgeList = new List<int>() { 25, 25, 26, 32, 27, 22, 42, 50, 23, 18, 51 };

// get the average age
double avg = AgeList.Average();

// output the results
Console.WriteLine(string.Format("Average value of list: {0}", avg));

// Outputs:
// Average value of list: 31

Another example of using LINQ Average is to find the average length of strings in a List. This example is taken from the Microsoft Documentation.

Calculating Average String Length of a List Using LINQ Average

string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" };
double average = fruits.Average(s => s.Length);
Console.WriteLine("The average string length is {0}.", average);
/*
 This code produces the following output:

 The average string length is 6.5.
*/ 

As we can see, LINQ Average allows use to use a Lambda expression also, for a more refined Average calculation.

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