How to Get the Index Position of the Results

Select and SelectMany expose an overload that surfaces the index position (starting at zero) for each returned element in the Select projection. It is surfaced as an overloaded parameter argument of the selector lambda expression and is only accessible using the extension method query syntax. Listing 3-9 demonstrates how to access and use the index position value in a Select projection. As shown in Output 3-6, this example simply adds a ranking number for each select result string.

Listing 3-9. A zero-based index number is exposed by the Select and SelectMany operators—see Output 3-6

List<CallLog> callLog = CallLog.SampleData();

var q = callLog.GroupBy(g => g.Number)
               .OrderByDescending(g => g.Count())
               .Select((g, index) => new
               {
                   number = g.Key,
                   rank = index + 1,
                   count = g.Count()
               });

foreach (var c in q)
    Console.WriteLine(
        "Rank {0} - {1}, called {2} times.",
        c.rank, c.number, c.count);