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();
int groupCount = groups.Count // 5