Given 2 C# Lists how to merge them and get only the non duplicated elements from both lists

Question

I have 2 lists in C#

List<int> list1 = new List<int> { 78, 92, 100, 37, 81 };
List<int> list2 = new List<int> { 3, 92, 1, 37 };

The expected result should be

{ 3, 78, 100, 1, 81 }

Please note! Duplicates: 92 and 37 doesn't appear anymore in the new list. The new list should have non duplicated elements from both lists.

Each list cannot have duplicated values. Ideally i would like to extend it to an object.

I can do it iterating manually both lists finding and removing duplicates.

My question is : Is there a more elegant and compact way to do in with .NET C# ?

[The opposite of Intersect()](//stackoverflow.com/q/5620266) — 001, Jul 12 '19 at 12:06
Possible duplicate of [how to merge 2 List with removing duplicate values in C#](https://stackoverflow.com/questions/4031262/how-to-merge-2-listt-with-removing-duplicate-values-in-c-sharp) — Md. Suman Kabir, Jul 12 '19 at 12:09

Dmitry Bychenko · Answer 1 · 2019-07-12T13:17:56.093

4

You are looking for SymmetricExceptWith or its emulation, e.g.

  HashSet<int> result = new HashSet<int>(list1);

  result.SymmetricExceptWith(list2);

Let's have a look at the items:

  Console.Write(string.Join(", ", result));

Outcome:

  78, 100, 81, 3, 1

If you want List<int> (not HashSet<int>) as a result, add ToList():

  List<int> final = result.ToList();

edited Jul 12 '19 at 13:17

answered Jul 12 '19 at 13:11

Dmitry Bychenko

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huMpty duMpty · Answer 2 · 2019-07-12T12:15:08.380

1

var result = list1.Concat(list2).
             GroupBy((g) => g).Where(d => d.Count() == 1).
             Select(d => d.Key).ToList();

edited Jul 12 '19 at 12:15

answered Jul 12 '19 at 12:05

huMpty duMpty

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score 1 · Answer 3 · edited Jul 12 '19 at 12:12

1

If you intersect both lists then subtract it from their union you will get the result:

var result = list1
    .Concat(list2)
    .Except(list1.Intersect(list2))
    .ToList();

edited Jul 12 '19 at 12:12

kara

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answered Jul 12 '19 at 12:08

DotNet Developer

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score 0 · Answer 4 · answered Jul 12 '19 at 12:08

0

You can use the Distinct() method from Linq, which, given a list containing duplicates, returns distinct elements from a sequence of integers. More on Distinct() here .

answered Jul 12 '19 at 12:08

Xander

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score 0 · Answer 5 · answered Jul 12 '19 at 12:11

List<int> list1 = new List<int> { 78, 92, 100, 37, 81 };
List<int> list2 = new List<int> { 3, 92, 1, 37 };

IEnumerable<int> result = list1
    .Concat(list2)              // Concat both lists to one big list. Don't use Union! It drops the duplicated values!
    .GroupBy(g => g)            // group them by values
    .Where(g => g.Count() == 1) // only values which have a count of 1
    .Select(s => s.Key);        // select the values

Console.WriteLine(string.Join(", ", result));

Given 2 C# Lists how to merge them and get only the non duplicated elements from both lists

5 Answers5

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