Intersect Two Lists in C#

c# intersection
Merni picture Merni · Aug 25, 2011 · Viewed 124.8k times · Source

I have two lists:

  List<int> data1 = new List<int> {1,2,3,4,5};
  List<string> data2 = new List<string>{"6","3"};

I want do to something like 

var newData = data1.intersect(data2, lambda expression);

The lambda expression should return true if data1[index].ToString() == data2[index]

Answer

George Duckett picture George Duckett · Aug 25, 2011

You need to first transform data1, in your case by calling ToString() on each element.

Use this if you want to return strings.

List<int> data1 = new List<int> {1,2,3,4,5};
List<string> data2 = new List<string>{"6","3"};

var newData = data1.Select(i => i.ToString()).Intersect(data2);

Use this if you want to return integers.

List<int> data1 = new List<int> {1,2,3,4,5};
List<string> data2 = new List<string>{"6","3"};

var newData = data1.Intersect(data2.Select(s => int.Parse(s));

Note that this will throw an exception if not all strings are numbers. So you could do the following first to check:

int temp;
if(data2.All(s => int.TryParse(s, out temp)))
{
    // All data2 strings are int's
}

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