How do you use LINQ to find the duplicate of a specific property?

Question

Customer customerOne = new Customer(\"John\", \"Doe\");
Customer customerTwo = new Customer(\"Super\", \"Man\");
Customer customerThree = new Customer(\"Crazy\", \"Guy\"         


        

Answer 1

var groups = customers.GroupBy(c => c.LastName).Where(g => g.Skip(1).Any());
foreach(var group in groups) {
    Console.WriteLine(group.Key);
    foreach(var customer in group) {
        Console.WriteLine("\t" + customer.FirstName);
    }
}

Output:

Doe
        John
        Jane
Man
        Super
        Bat

You can flatten the resulting sequence of groups into one sequence with

var list = groups.SelectMany(g => g);