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Home Forums Why C# LINQ Distinct() doesn’t work? – MindStick
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1 Answers

Aryan Kumar
Aryan Kumar 18 Aug 2023
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The Distinct() method in LINQ is used to remove duplicates from a sequence. The Distinct() method takes an optional parameter that specifies the comparer to use when comparing elements. If the parameter is 0, the default comparer is used. The default comparer compares elements by their GetHashCode() method.

The GetHashCode() method returns a hash code for an object. The hash code is used to quickly compare elements in a hash table. However, the GetHashCode() method does not guarantee that two objects with different values will have different hash codes. This is why the Distinct() method with a parameter of 0 does not work.

To use the Distinct() method to remove duplicates, you need to specify a comparer that guarantees that two objects with different values will have different hash codes. You can use the IEqualityComparer interface to create a custom comparer.

The following code is an example of how to use the Distinct() method with a custom comparer:

C#

public class Person {
    public string Name { get; set; }
}

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

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

var people = new List<Person>();
people.Add(new Person { Name = "John" });
people.Add(new Person { Name = "Jane" });
people.Add(new Person { Name = "John" });

var distinctPeople = people.Distinct(new PersonComparer());

In this code, the PersonComparer class implements the IEqualityComparer interface and provides a custom comparer for the Person class. The Equals() method compares the names of two Person objects and returns a value indicating whether the two objects are equal. The GetHashCode() method returns a hash code for a Person object.

The distinctPeople variable is a list that contains only the distinct Person objects from the people list.

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