Get the number of distinct property values in List<T> using LINQ in C#

Question

In a list List<MyClass> ListOfMyClasses, how can one get the how many distinct GroupId property values there are using LINQ?

public class MyClass
{
     public int GroupId;
}

For example let's say we have this list:

ListOfMyClasses: {MyClass1 (GroupId = 1), MyClass2 (GroupId = 3), MyClass3 (GroupId = 1)}

Here we should get the result as 2 (Two distinct numbers for GroupId).

Answer 1

Here is one way to do it using Distinct:

ListOfMyClasses.Select(t => t.GroupId).Distinct().Count()

Or you can also use GroupBy:

ListOfMyClasses.GroupBy(t => t.GroupId).Count()

Answer 2

This should work for you.

var result = list.Select(x => x.GroupId).Distinct().Count();

First you are selecting out all the GroupIds. Then you are filtering them to be distinct. Finally you are getting the count of those values.