linq - Compare two lists C#

Question

I am having two lists

List<int> a = {1,2,3};
List<int> b = {3,4};

I need to compare them in such a way that the output should be

1 false
2 false
4 true

The output is by using the following logic

• 1,2 are in a but not in b so they are set to false whereas
• 3 is in both the lists so its not in the output and
• '4' is in b but not in a so they are set to true

the return type is a List<modelClass> that has int id, bool isTrue properties

Can you help me?

Answer 1

If you don't care about performance you can use the following LINQ:

a.Except(b)
  .Union(b.Except(a))
  .Select(item => new { id = item, isTrue = b.Contains(item) });

With HashSet usage:

var setA = new HashSet<int>(a);
var setB = new HashSet<int>(b);
setA.SymmetricExceptWith(b);

var result = setA.Select(item => new { id = item, isTrue = setB.Contains(item) });