LINQ Distinct

LINQ Distinct is a method that returns unique elements from a sequence. This method is used to remove duplicates from a collection or a list.

The syntax of the Distinct method is as follows:

IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source)

Where source is an IEnumerable of a specific data type TSource.

Example

Consider the following list of integers:

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

We want to remove duplicates from this list using the Distinct method. Let's see how this can be done:

var uniqueNumbers = numbers.Distinct();

The resulting uniqueNumbers variable contains:

1, 2, 3, 4, 5

Custom Comparer

The Distinct method uses the default equality comparer to check for duplicates. However, you can create a custom comparer to compare objects based on specific criteria.

For example, consider the following class:

public class Person
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

We want to remove duplicates from a list of persons based on their Name property. We can create a custom comparer as follows:

public class PersonNameComparer : IEqualityComparer<Person>
{
    public bool Equals(Person x, Person y)
    {
        return x.Name == y.Name;
    }

    public int GetHashCode(Person obj)
    {
        return obj.Name.GetHashCode();
    }
}

To use this custom comparer with the Distinct method, we need to pass it as a parameter:

List<Person> persons = new List<Person>
{
    new Person { Id = 1, Name = "John", Age = 30 },
    new Person { Id = 2, Name = "Mary", Age = 25 },
    new Person { Id = 3, Name = "John", Age = 35 }
};

var uniquePersons = persons.Distinct(new PersonNameComparer());

The resulting uniquePersons variable contains:

John, Mary

Conclusion

The Distinct method is a useful LINQ method that helps remove duplicates from a collection or a list. It can also be used with a custom comparer to compare objects based on specific criteria.