How do you calculate collections with Aggregate operator?

1 What is the Aggregate operator?

The Aggregate operator is a LINQ extension method that takes a collection of elements and applies a function to each element and an accumulator value, starting from the first element and ending with the last one. The result of each function application is stored in the accumulator and returned as the final output. For example, if you have a collection of numbers and you want to find their sum, you can use the Aggregate operator with a function that adds each element to the accumulator.

2 How to use the Aggregate operator with LINQ to Objects?

LINQ to Objects is a way of using LINQ queries on any collection that implements the IEnumerable<T> interface, such as arrays, lists, or dictionaries. To use the Aggregate operator with LINQ to Objects, you need to import the System.Linq namespace and call the Aggregate extension method on your collection. For example, if you have an array of integers called numbers, you can find their sum by writing:

using System.Linq;
int[] numbers = { 1, 2, 3, 4, 5 };
int sum = numbers.Aggregate((a, b) => a + b); // sum is 15        

3 How to use the Aggregate operator with LINQ to Collections?

LINQ to Collections is a way of using LINQ queries on collections that implement the IQueryable<T> interface, such as Entity Framework or LINQ to SQL. To use the Aggregate operator with LINQ to Collections, you need to use the same syntax as with LINQ to Objects, but be aware that the function you pass to the operator may be translated to SQL or another query language, depending on the provider. For example, if you have a DbSet of Products in your Entity Framework context, you can find the average price of all products by writing:

using System.Linq;
DbSet<Product> products = context.Products;
decimal averagePrice = products.Aggregate((a, b) => a + b.Price) / products.Count(); // averagePrice is the total price divided by the number of products        

4 How to use custom functions with the Aggregate operator?

The function you pass to the Aggregate operator can be any lambda expression or delegate that takes two parameters of the same type as the elements in your collection and returns a value of the same type. This means you can use custom functions to perform any calculation you want on your collection, as long as they follow this signature. For example, if you want to find the longest word in a collection of strings, you can use a function that compares the lengths of two strings and returns the longer one:

using System.Linq;
string[] words = { "hello", "world", "linq", "aggregate" };
string longestWord = words.Aggregate((a, b) => a.Length > b.Length ? a : b); // longestWord is "aggregate"        

5 How to use seed values with the Aggregate operator?

The Aggregate operator has an overload that takes a seed value as the first parameter. The seed value is the initial value of the accumulator and can be any type you want. The function you pass to the operator must then take two parameters: one of the same type as the seed value and one of the same type as the elements in your collection. The function must also return a value of the same type as the seed value. The seed value can be useful when you want to perform calculations that involve different types or start from a different base. For example, if you want to concatenate all the strings in a collection with a comma separator, you can use an empty string as the seed value and a function that appends a comma and an element to the accumulator:

using System.Linq;
string[] words = { "hello", "world", "linq", "aggregate" };
string concatenated = words.Aggregate("", (a, b) => a + "," + b); // concatenated is ",hello,world,linq,aggregate"        

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?