Add elements from one list to another C#

Question

What is the simplest way to add elements of one list to another?

For example, I have two lists:

List A which contains x items List B which contains y items.

I want to add elements of B to A so that A now contains X+Y items. I know this can done using a loop but is there a built in method for this? Or any other technique?

Answer 1

Your question describes the List.AddRange method, which copies all the elements of its argument into the list object on which it is called.

As an example, the snippet

List<int> listA = Enumerable.Range(0, 10).ToList(); List<int> listB = Enumerable.Range(11, 10).ToList(); Console.WriteLine("Old listA: [{0}]", string.Join(", ", listA)); Console.WriteLine("Old listB: [{0}]", string.Join(", ", listB)); listA.AddRange(listB); Console.WriteLine("New listA: [{0}]", string.Join(", ", listA)); 

prints

Old listA: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] Old listB: [11, 12, 13, 14, 15, 16, 17, 18, 19, 20] New listA: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20] 

showing that all the elements of listB were added to listA in the AddRange call.

Answer 2

To join two lists, you can do

listA.AddRange(listB); // listA will contain x+y items 

or

// listC contains x+y items, listA and listB are unchanged. var listC = listA.Concat(listB);  

You could use the latter to reassign listA instead:

listA = listA.Concat(listB).ToList(); 

but there isn't any particular advantage to that over AddRange if you're okay with modifying one of the original lists in the first place.