LINQ GroupBy Operator in C# with Examples

The GroupBy operator is a LINQ query operator that groups the elements of a sequence according to a specified key. The key is specified by a function that takes an element of the sequence as input and returns a value that is used to determine the group to which the element belongs.

Here are some examples of how you might use the GroupBy operator in C#:

Example 1: Grouping a list of integers by their remainder when divided by a specific number:


List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
var groupedNumbers = numbers.GroupBy(n => n % 3);

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var groupedNumbers = numbers.GroupBy(n => n % 3);

Example 2: Grouping a list of strings by their first letter:


List<string> words = new List<string> { "apple", "banana", "cherry", "date", "elderberry" };
var groupedWords = words.GroupBy(w => w[0]);

List<string> words = new List<string> { "apple", "banana", "cherry", "date", "elderberry" };

var groupedWords = words.GroupBy(w => w[0]);

Example 3: Grouping a list of objects by a specific property:


List<Product> products = GetProducts();
var groupedProducts = products.GroupBy(p => p.Category);

List<Product> products = GetProducts();

var groupedProducts = products.GroupBy(p => p.Category);

Example 4: Grouping a list of objects by multiple properties:


List<Order> orders = GetOrders();
var groupedOrders = orders.GroupBy(o => new { o.Customer.Country, o.Customer.City });

List<Order> orders = GetOrders();

var groupedOrders = orders.GroupBy(o => new { o.Customer.Country, o.Customer.City });

Example 5: Grouping a list of objects by a specific property and then sorting the groups by another property:


List<Employee> employees = GetEmployees();
var groupedEmployees = employees.GroupBy(e => e.Department)
                                .OrderBy(g => g.Key)
                                .Select(g => new { Department = g.Key, Employees = g });

List<Employee> employees = GetEmployees();

var groupedEmployees = employees.GroupBy(e => e.Department)

.OrderBy(g => g.Key)

.Select(g => new { Department = g.Key, Employees = g });

In these examples, the GroupBy operator is used to group the elements of a sequence according to a specified key. The key is specified by a function that takes an element of the sequence as input and returns a value that is used to determine the group to which the element belongs.

In the first example, the GroupBy operator is used to group a list of integers by their remainder when divided by a specific number. In the second example, the GroupBy operator is used to group a list of strings by their first letter. In the third example, the GroupBy operator is used to group a list of Product objects by the Category property. In the fourth example, the GroupBy operator is used to group a list of Order objects by multiple properties Country and City. In the fifth example, the GroupBy operator is used to group a list of Employee objects by the Department property, OrderBy operator is used to sort the groups by the Department property and the Select operator is used to create a new sequence of anonymous objects that contain the department and the group of employees.

It’s worth noting that GroupBy operator returns an IEnumerable<IGrouping<TKey, TElement>>, which is a sequence of IGrouping<TKey, TElement> objects, where TKey is the type of the key and TElement is the type of the elements in the group.

LINQ GroupBy Operator in C# with Examples

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