SelectMany - Indexed

Query

public void Linq19()
{
    List customers = GetCustomerList();
  
    var customerOrders =
        customers.SelectMany(
            (cust, custIndex) =>
            cust.Orders.Select(o => "Customer #" + (custIndex + 1) +
                                    " has an order with OrderID " + o.OrderID));
  
    ObjectDumper.Write(customerOrders);
}

Lambda Expression

public void DataSetLinq19()
{
    var customers = testDS.Tables["Customers"].AsEnumerable();
    var orders = testDS.Tables["Orders"].AsEnumerable();
 
    var customerOrders =
        customers.SelectMany(
            (cust, custIndex) =>
            orders.Where(o => cust.Field("CustomerID") == o.Field("CustomerID"))
                .Select(o => new { CustomerIndex = custIndex + 1, OrderID = o.Field("OrderID") }));
 
    foreach (var c in customerOrders)
    {
        Console.WriteLine("Customer Index: " + c.CustomerIndex +
                            " has an order with OrderID " + c.OrderID);
    }
}

Output

Customer #1 has an order with OrderID 10643
Customer #1 has an order with OrderID 10692
Customer #1 has an order with OrderID 10702
Customer #1 has an order with OrderID 10835
Customer #1 has an order with OrderID 10952
Customer #1 has an order with OrderID 11011
Customer #2 has an order with OrderID 10308
Customer #2 has an order with OrderID 10625
Customer #2 has an order with OrderID 10759
Customer #2 has an order with OrderID 10926

...
Customer #90 has an order with OrderID 10248
Customer #90 has an order with OrderID 10615
Customer #90 has an order with OrderID 10673
Customer #90 has an order with OrderID 10695
Customer #90 has an order with OrderID 10873
Customer #90 has an order with OrderID 10879
Customer #90 has an order with OrderID 10910
Customer #90 has an order with OrderID 11005
Customer #91 has an order with OrderID 10374
Customer #91 has an order with OrderID 10611
Customer #91 has an order with OrderID 10792
Customer #91 has an order with OrderID 10870
Customer #91 has an order with OrderID 10906
Customer #91 has an order with OrderID 10998
Customer #91 has an order with OrderID 11044