C# 0 The Complete Reference

Name

 and 

InStock

, just as before. The compiler 

automatically “projects” the identifiers 

Name

 and 

InStock

, making them the property 

names of the anonymous type. Also as before, the properties are given the values specified 

by

item.Name

and

entry.InStock

.

Create a Group Join

As explained earlier, you can use 

into

 with 

join

 to create a 

group join,

 which creates a 

sequence in which each entry in the result consists of an entry from the first sequence and 

a group of all matching elements from the second sequence. No example was presented 

then because often a group join makes use of an anonymous type. Now that anonymous 

types have been covered, an example of a simple group join can be given.

The following example uses a group join to create a list in which various transports, such 

as cars, boats, and planes, are organized by their general transportation category, which is 

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P a r t   I :  

T h e   C #   L a n g u a g e

land, sea, and air. The program first creates a class called 

Transport

 that links a transport 

type with its classification. Inside 

Main( )

, it creates two input sequences. The first is an array 

of strings that contains the names of the general means by which one travels, which is land, 

sea, and air. The second is an array of 

Transport

, which encapsulates various means of 

transportation. It then uses a group join to produce a list of transports that are organized 

by their category.

// Demonstrate a simple group join.

using System;

using System.Linq;

// This class links the name of a transport, such as Train,

// with its general classification, such as land, sea, or air.

class Transport {

  public string Name { get; set; }

  public string How { get; set; }

  public Transport(string n, string h) {

    Name = n;

    How = h;

  }

}

class GroupJoinDemo {

  static void Main() {

    // An array of transport classifications.

    string[] travelTypes = {

         "Air",

         "Sea",

         "Land"

    };

    // An array of transports.

    Transport[] transports = {

         new Transport("Bicycle", "Land"),

         new Transport("Balloon", "Air"),

         new Transport("Boat", "Sea"),

         new Transport("Jet", "Air"),

         new Transport("Canoe", "Sea"),

         new Transport("Biplane", "Air"),

         new Transport("Car", "Land"),

         new Transport("Cargo Ship", "Sea"),

         new Transport("Train", "Land")

    };

    // Create a query that uses a group join to produce

    // a list of item names and IDs organized by category.

    var byHow = from how in travelTypes

                       join trans in transports

                       on how equals trans.How

                       into lst

                     select new { How = how, Tlist = lst };

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