.NET 4.0 Generics

Time for action – one-to-many mapping

Here is the first problem:

Suppose, we have a List of names and we want to index them as per the first two letters of these names:

1. Copy the following code snippet as a query to LINQPad:

   string[] firstNames = { "Samuel", "Jenny", "Joyace", "Sam" };
   var map = firstNames.ToLookup(c => c.Length);
   foreach (var m in map)
   {
     Console.WriteLine(m.Key);
     foreach (var n in m)
     {
       Console.WriteLine("--" + n);
     }
   }

2. Run the query and you should get the following output:
   

What just happened?

ToLookup() creates what you can imagine as a one-to-many Dictionary.

The Lambda expression c => c.Length describes the key to be used for the ...