C# 0 The Complete Reference

.org

 or 

.com

.

// Demonstrate the group clause.

using System;

using System.Linq;

class GroupDemo {

  static void Main() {

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    string[] websites = { "hsNameA.com", "hsNameB.net", "hsNameC.net",

                          "hsNameD.com", "hsNameE.org", "hsNameF.org",

                          "hsNameG.tv",  "hsNameH.net", "hsNameI.tv" };

    // Create a query that groups websites by top-level domain name.

    var webAddrs = from addr in websites

                   where addr.LastIndexOf(".") != -1

                   group addr by addr.Substring(addr.LastIndexOf("."));

    // Execute the query and display the results.

    foreach(var sites in webAddrs) {

      Console.WriteLine("Web sites grouped by " + sites.Key);

      foreach(var site in sites)

        Console.WriteLine("  " + site);

      Console.WriteLine();

    }

  }

}

The output is shown here:

Web sites grouped by .com

  hsNameA.com

  hsNameD.com

Web sites grouped by .net

  hsNameB.net

  hsNameC.net

  hsNameH.net

Web sites grouped by .org

  hsNameE.org

  hsNameF.org

Web sites grouped by .tv

  hsNameG.tv

  hsNameI.tv

As the output shows, the data is grouped based on the top-level domain name of a 

website. Notice how this is achieved by the 

group

 clause:

var webAddrs = from addr in websites

               where addr.LastIndexOf(".") != -1

               group addr by addr.Substring(addr.LastIndexOf("."));

The key is obtained by use of the