Question

I got a list:

var list = new List<List<int>>();

which could contain

list[0] = {1, 2, 3, 4}
list[1] = {3, 1, 2, 4}
list[2] = {2, 1, 7, 3}

How can I detect the duplicate between [0] and [1] and remove one of them? Code is c-sharp.

In reality it’s not a int, but that shouldn’t change the question.

Answer 1

You could write your own implementation of IEqualityComparer<List<int>>. For GetHashCode() it would simply return the XOR of all the hash codes of the elements in the list. For Equals() it would create a new HashSet<int> from the first list, and call HashSet<T>.SetEquals on it, passing in the second list. This assumes there will be no duplicate elements, mind you. (Otherwise { 1, 1, 2 } will be equal to { 1, 2, 2 } but have a different hash code.)

Once you’ve got that far, you can use Distinct:

var distinct = list.Distinct(new CustomEqualityComparer());

As an alternative approach, could you use HashSet<T> as your collection type to start with? Then it’s really easy:

var distinct = sets.Distinct(HashSet<int>.CreateSetComparer());

If you need lists as the input but can cope with sets as the output:

var distinct = list.Select(x => new HashSet<int>(x))
                   .Distinct(HashSet<int>.CreateSetComparer());