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How to use Group by in LINQ?

Steilla Mitchel 191 17-Aug-2023

How to use Group by in LINQ?

c# linq

Updated on 18-Aug-2023

Steilla Mitchel

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I completed my post-graduation in 2013 in the engineering field. Engineering is the application of science and math to solve problems. Engineers figure out how things work and find practical uses for scientific discoveries. Scientists and inventors often get the credit for innovations that advance the human condition, but it is engineers who are instrumental in making those innovations available to the world. I love pet animals such as dogs, cats, etc.

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Aryan Kumar

18-Aug-2023

The GroupBy() method in LINQ is used to group elements in a sequence based on a common property. The GroupBy() method returns a IGrouping<TKey, TResult> object, which is a collection of elements that have the same key.

The syntax for the GroupBy() method is as follows:

sequence.GroupBy(keySelector, [elementSelector])

sequence: The sequence of elements to be grouped.
keySelector: A delegate that returns the key for each element.
elementSelector: An optional delegate that returns the element to be included in the group.

The keySelector delegate is required. The elementSelector delegate is optional. If the elementSelector delegate is not specified, the entire element is used as the group key.

The following code groups a list of Person objects by their age:

var people = new List<Person>();
people.Add(new Person { Age = 20, Name = "John" });
people.Add(new Person { Age = 30, Name = "Jane" });
people.Add(new Person { Age = 10, Name = "Peter" });

var groupedPeople = people.GroupBy(p => p.Age);

In this code, the GroupBy() method groups the people list by the Age property of the Person objects. The groupedPeople variable is a IGrouping<int, Person> object, which is a collection of Person objects that have the same age.

To iterate through the groupedPeople object, you can use a foreach loop:

foreach (var group in groupedPeople) {
    Console.WriteLine(group.Key);
    foreach (var person in group) {
        Console.WriteLine(person.Name);
    }
}

In this code, the foreach loop iterates through the groupedPeople object and prints the age and name of each person in the group.

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How to use Group by in LINQ?

Steilla Mitchel

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