LINQ Aggregation: Sum, Count, Average

Syntax

collection.Sum() / .Count() / .Average() / .Max() / .Min()

Examples

List<int> scores = new List<int> { 85, 92, 78, 90, 88 };

Console.WriteLine(scores.Count());    // 5
Console.WriteLine(scores.Sum());       // 433
Console.WriteLine(scores.Average());   // 86.6
Console.WriteLine(scores.Max());        // 92
Console.WriteLine(scores.Min());        // 78

record Product(string Name, double Price);

List<Product> cart = new List<Product>
{
    new Product("Keyboard", 25),
    new Product("Mouse", 15),
    new Product("Monitor", 200)
};

double total = cart.Sum(p => p.Price);
Console.WriteLine(total);  // 240

Product mostExpensive = cart.MaxBy(p => p.Price)!;
Console.WriteLine(mostExpensive.Name);  // Monitor

List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

int product = numbers.Aggregate(1, (acc, n) => acc * n);
Console.WriteLine(product);  // 120

string combined = numbers.Aggregate("", (acc, n) => acc + n + "-");
Console.WriteLine(combined);  // 1-2-3-4-5-

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8 };

int evenCount = numbers.Count(n => n % 2 == 0);
Console.WriteLine(evenCount);  // 4

Best practices

• Use the selector overload (Sum(x => x.Property)) directly rather than chaining a separate Select() first - it is more concise and avoids an intermediate sequence
• Use Count(predicate) instead of Where(predicate).Count() to skip creating an intermediate filtered sequence
• Reach for Aggregate() only when the built-in Sum/Count/Average/Max/Min genuinely don't cover your accumulation logic - it is less readable for simple cases
• Handle empty sequences carefully - Average(), Max(), and Min() throw an exception on an empty sequence, so check .Any() first or use the null-returning "OrDefault" variants where available

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation