CODEWITHSUNDEEP
c#.netlinqlistunion
RSK
RSK

Reputation: 2221

Simplest way to form a union of two lists

What is the easiest way to compare the elements of two lists say A and B with one another, and add the elements which are present in B to A only if they are not present in A?

To illustrate, Take list A = {1,2,3} list B = {3,4,5}

So after the operation AUB I want list A = {1,2,3,4,5}

Upvotes: 94

Views: 155946

Answers (5)

Mikael Engver
Mikael Engver

Reputation: 4768

If it is two IEnumerable lists you can't use AddRange, but you can use Concat.

IEnumerable<int> first = new List<int>{1,1,2,3,5};
IEnumerable<int> second = new List<int>{8,13,21,34,55};

var allItems = first.Concat(second);
// 1,1,2,3,5,8,13,21,34,55

Upvotes: 1

Tilak
Tilak

Reputation: 30698

If it is a list, you can also use AddRange method.

var listB = new List<int>{3, 4, 5};  
var listA = new List<int>{1, 2, 3, 4, 5};

listA.AddRange(listB); // listA now has elements of listB also.

If you need new list (and exclude the duplicate), you can use Union

  var listB = new List<int>{3, 4, 5};  
  var listA = new List<int>{1, 2, 3, 4, 5};
  var listFinal = listA.Union(listB);

If you need new list (and include the duplicate), you can use Concat

  var listB = new List<int>{3, 4, 5};  
  var listA = new List<int>{1, 2, 3, 4, 5};
  var listFinal = listA.Concat(listB);

If you need common items, you can use Intersect.

var listB = new List<int>{3, 4, 5};  
var listA = new List<int>{1, 2, 3, 4};  
var listFinal = listA.Intersect(listB); //3,4

Upvotes: 187

Prabhu Murthy
Prabhu Murthy

Reputation: 9261

Using LINQ's Union

Enumerable.Union(ListA,ListB);

or

ListA.Union(ListB);

Upvotes: 11

code4life
code4life

Reputation: 15794

I think this is all you really need to do:

var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4, 5};

var listMerged = listA.Union(listB);

Upvotes: 5

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726599

The easiest way is to use LINQ's Union method:

var aUb = A.Union(B).ToList();

Upvotes: 31

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