C#: Compare contents of two IEnumerables

Question

Is there a built in linq method thing I can use to find out if two sequences contains the same items, not taking the order into account?

For example:

{1, 2, 3} == {2, 1, 3}
{1, 2, 3} != {2, 1, 3, 4}
{1, 2, 3} != {1, 2, 4}

You have the SequenceEquals, but then I would have to Order both sequences first, wouldn't I?

Answer 1

I think ordering the sequence is the fastest way you can achieve this.

Answer 2

There are quite a few ways. Assume A and B is IEnumerable.

A.Except(B).Count == 0 && B.Except(A).Count == 0
A.Count == B.Count && A.Intersect(B).Count == B.Count
etc

Answer 3

I did this for merging new items into a collection without duplicates, it takes two collections and returns all the items with out any duplicates

List<Campaign> nonMatching = (from n in newCampaigns 
where !(from e in Existing select e.Id).Contains<int>(n.Id) 
select n).ToList<Campaign>();

Now by removing the ! for the contains statement

List<Campaign> nonMatching = (from n in newCampaigns 
where (from e in Existing select e.Id).Contains<int>(n.Id) 
select n).ToList<Campaign>();

it will return the duplicates

Answer 4

If you're really just testing to see if there are duplicates, then leppie's suggestion should work:

if (A.Except(B).Count == 0 && B.Except(A).Count == 0) {...}

But if you just need to arrive at an IEnumerable with no duplicates:

var result = A.Union(B).Distinct();

Answer 5

Try the HashSet class:

var enumA = new[] { 1, 2, 3, 4 };
var enumB = new[] { 4, 3, 1, 2 };

var hashSet = new HashSet<int>(enumA);
hashSet.SymmetricExceptWith(enumB);
Console.WriteLine(hashSet.Count == 0); //true => equal

But that does only work correctly if the values are distinct.

For example

var enumA = new[] { 1, 1, 1, 2 };
var enumB = new[] { 1, 2, 2, 2 };

are also considered as "equal" wit the mentioned method.