C# 0 The Complete Reference

descending

 option, as shown here:

var posNums = from n in nums

              orderby n descending

              select n;

If you try this, you will see that the order of the values is reversed.

Although sorting on a single criterion is often what is needed, you can use 

orderby

 to 

sort on multiple items by using this form:

orderby 

sort-onA direction

,

sort-onB direction

,

sort-onC direction

, …

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In this form, 

sort-onA

 is the item on which the primary sorting is done. Then, each group of 

equivalent items is sorted on 

sort-onB

, and each of those groups is sorted on 

sort-onC

, and so 

on. Thus, each subsequent 

sort-on

 specifies a “then by” item on which to sort. In all cases, 

direction

 is optional, defaulting to 

ascending

. Here is an example that uses three sort criteria 

to sort bank account information by last name, then by first name, and finally by account 

balance:

// Sort on multiple criteria with orderby.

using System;

using System.Linq;

class Account {

  public string FirstName { get; private set; }

  public string LastName { get; private set; }

  public double Balance { get; private set; }

  public string AccountNumber { get; private set; }

  public Account(string fn, string ln, string accnum, double b) {

    FirstName = fn;

    LastName = ln;

    AccountNumber = accnum;

    Balance = b;

  }

}

class OrderbyDemo {

  static void Main() {

    // Create some data.

    Account[] accounts = { new Account("Tom", "Smith", "132CK", 100.23),

                           new Account("Tom", "Smith", "132CD", 10000.00),

                           new Account("Ralph", "Jones", "436CD", 1923.85),

                           new Account("Ralph", "Jones", "454MM", 987.132),

                           new Account("Ted", "Krammer", "897CD", 3223.19),

                           new Account("Ralph", "Jones", "434CK", -123.32),

                           new Account("Sara", "Smith", "543MM", 5017.40),

                           new Account("Sara", "Smith", "547CD", 34955.79),

                           new Account("Sara", "Smith", "843CK", 345.00),

                           new Account("Albert", "Smith", "445CK", 213.67),

                           new Account("Betty", "Krammer","968MM",5146.67),

                           new Account("Carl", "Smith", "078CD", 15345.99),

                           new Account("Jenny", "Jones", "108CK", 10.98)

                         };

    // Create a query that obtains the accounts in sorted order.

    // Sorting first by last name, then within same last names sorting by

    // by first name, and finally by account balance.

    var accInfo = from acc in accounts

                  orderby acc.LastName, acc.FirstName, acc.Balance

                  select acc;

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