How to eliminate duplicates with LINQ UNION

Eliminate duplicate values with LINQ UNION

There is a possible to have duplicate entries in the output list When using the LINQ ‘UNION’ operation to join two list object. There are couple of ways to overcome this issue. 

The solution here we are going to discuss is with IEqualityComparer.

In this example we are going to do a union of two employee objects.

Add a class to implement IEqualityComparer as follows

class EmployeeComparer : IEqualityComparer<Employee>

{
       public bool Equals(Employee e1, Employee e2)
       {
               return e1.Number == e2.Number;
       }
       public int GetHashCode(Employee e)
       {
               return e.Number;
       }
}

Then just add it as the second parameter to the constructor. var merged = employeeList1.Union(employeeList2, new EmployeeComparer());