Grouping

List<Customer> customers = new()
            {
                new Customer(1, "Jeff", "New York"),
                new Customer(2, "Harvey", "Los Angeles"),
                new Customer(3, "Donald", "New York"),
                new Customer(4, "Megan", "Toronto"),
                new Customer(5, "Frank", "New York"),
            };

            List<IGrouping<object, Customer>> groups = customers.GroupByMany(x => x.Name, x => x.Address).ToList();
            Assert.IsTrue(groups.Count == 5);

int groupCount = groups.FirstOrDefault(x => 
                  {
                    object[] keys = x.Key as object[];
                    return (string)keys[0] == "Jeff" && (string)keys[1] == "New York";
                  })
                  .Count(); // Returns 1