CsharpHow-ToBeginner · 3 min read

How to Use LINQ Average in C# for Calculating Averages

Use the Average() method from LINQ to calculate the average of numeric values in a collection. It works on arrays, lists, or any enumerable of numbers and returns the mean as a double. You can also use it with a selector function to average specific properties of objects.

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Syntax

The Average() method is called on a collection of numbers or objects. It can be used in two main ways:

Without selector: Calculates average of numeric values directly.
With selector: Calculates average of a numeric property from each object.

Example syntax:

var avg = collection.Average();
var avgProperty = collection.Average(item => item.Property);

csharp

var avg = collection.Average();
var avgProperty = collection.Average(item => item.Property);

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Example

This example shows how to calculate the average of numbers in an array and the average of a property in a list of objects.

csharp

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] numbers = { 10, 20, 30, 40, 50 };
        double averageNumbers = numbers.Average();
        Console.WriteLine($"Average of numbers: {averageNumbers}");

        var students = new List<Student>
        {
            new Student { Name = "Alice", Score = 85 },
            new Student { Name = "Bob", Score = 90 },
            new Student { Name = "Charlie", Score = 78 }
        };
        double averageScore = students.Average(s => s.Score);
        Console.WriteLine($"Average score: {averageScore}");
    }
}

class Student
{
    public string Name { get; set; }
    public int Score { get; set; }
}

Output

Average of numbers: 30 Average score: 84.3333333333333

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Common Pitfalls

Common mistakes when using Average() include:

Calling Average() on an empty collection causes an InvalidOperationException.
Using Average() on non-numeric types without a selector will not compile.
Not handling null values in collections of nullable types can cause exceptions.

To avoid errors, check if the collection has elements before calling Average() or use DefaultIfEmpty() to provide a default value.

csharp

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] empty = { };
        // This will throw InvalidOperationException
        // double avgEmpty = empty.Average();

        // Safe way:
        double avgSafe = empty.DefaultIfEmpty(0).Average();
        Console.WriteLine($"Safe average of empty array: {avgSafe}");
    }
}

Output

Safe average of empty array: 0

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Quick Reference

Usage	Description
collection.Average()	Calculates average of numeric values in collection
collection.Average(item => item.Property)	Calculates average of a numeric property in objects
collection.DefaultIfEmpty(0).Average()	Calculates average safely on possibly empty collection
Throws InvalidOperationException	If collection is empty and no default is provided

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Key Takeaways

Use LINQ's Average() to easily calculate the mean of numeric collections.

Provide a selector function to average specific properties of objects.

Avoid calling Average() on empty collections without a default value to prevent exceptions.

Use DefaultIfEmpty() to supply a default value when collections might be empty.

Average() returns a double representing the mean value.