Intersect Two Lists in C#

Question

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 1

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); 

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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 } 

Answer 2

If you have objects, not structs (or strings), then you'll have to intersect their keys first, and then select objects by those keys:

var ids = list1.Select(x => x.Id).Intersect(list2.Select(x => x.Id)); var result = list1.Where(x => ids.Contains(x.Id));