How to apply Group By in LINQ?

 In LINQ, you can use the Group By clause to group a collection of elements based on a specific key or property. The Group By clause returns a sequence of groupings, where each grouping consists of a key and a sequence of elements that share the same key.

Here's an example of using Group By in LINQ:

csharp
// create a collection of objects
List<Person> people = new List<Person>
{
    new Person { Name = "Alice", Age = 25 },
    new Person { Name = "Bob", Age = 30 },
    new Person { Name = "Charlie", Age = 25 },
    new Person { Name = "David", Age = 30 },
    new Person { Name = "Eva", Age = 25 }
};

// group people by age
var groupedPeople = from p in people
                    group p by p.Age;

// iterate through each group and its elements
foreach (var group in groupedPeople)
{
    Console.WriteLine("Age: " + group.Key);
    foreach (var person in group)
    {
        Console.WriteLine("  " + person.Name);
    }
}

In this example, we first create a collection of Person objects. We then use the group keyword in a LINQ query to group the people by their age property. This creates a sequence of groupings, where each grouping has a key (the age) and a sequence of elements (the people with that age).

We then iterate through each group and its elements using a foreach loop, printing out the age and the names of the people in each group.

The output of this code will be:

makefile
Age: 25
  Alice
  Charlie
  Eva
Age: 30
  Bob
  David

As you can see, the people have been grouped by their age, and the output shows each age and the names of the people with that age.