How do you concatenate Lists in C#?

c# arrays list concatenation
Matt picture Matt · Jun 25, 2009 · Viewed 239.3k times · Source

If I have:

List<string> myList1;
List<string> myList2;

myList1 = getMeAList();
// Checked myList1, it contains 4 strings

myList2 = getMeAnotherList();
// Checked myList2, it contains 6 strings

myList1.Concat(myList2);
// Checked mylist1, it contains 4 strings... why?

I ran code similar to this in Visual Studio 2008 and set break points after each execution. After myList1 = getMeAList();, myList1 contains four strings, and I pressed the plus button to make sure they weren't all nulls.

After myList2 = getMeAnotherList();, myList2 contains six strings, and I checked to make sure they weren't null... After myList1.Concat(myList2); myList1 contained only four strings. Why is that?

Answer

John Kugelman picture John Kugelman · Jun 25, 2009

Concat returns a new sequence without modifying the original list. Try myList1.AddRange(myList2).

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