C# 0 The Complete Reference

GroupBy( )

 method. It reworks the 

group

example shown earlier.

// Demonstrate the GroupBy() query method.

// This program reworks the earlier version that used

// the query syntax.

using System;

using System.Linq;

class GroupByDemo {

  static void Main() {

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

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

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

    // Use query methods to group websites by top-level domain name.

    var webAddrs = websites.Where(w => w.LastIndexOf(".") != 1).

           GroupBy(x => x.Substring(x.LastIndexOf(".", x.Length)));

    // 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();

    }

  }

}

This version produces the same output as the earlier version. The only difference is how the 

query is created. In this version, the query methods are used.

Here is another example. Recall the 

join

 query used in the 

JoinDemo

 example shown 

earlier:

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