Beginning C# 2008-from Novice-to-professional - A2Z Dotnet

426CHAPTER 15 ■ LEARNING ABOUT LINQThe ideas of LINQ that include from, where, and select are not lost; they just have not beenused. The from part is the _tickets variable itself. The where part is the method Where(), andthe select part is a default selection of the currently selected node.To specify an action with Where(), you use a lambda expression, which has two parameters:the object and the index of the object. The lambda expression expects that you return a Booleanvalue indicating whether the ticket item should be added to a returned list.When you use the list methods associated with the type, you are using a different functionalitythan LINQ in the abstract sense. LINQ is a syntax that wraps SQL-like text. LINQ ismuch easier to understand and program. Using the methods gives you more flexibility, butthey also are more complicated to write.For example, if you wanted to find the frequency of two numbers in a list, you could usethis code:int FrequencyOfTwoNumbersList(int number1ToSearch, int number2ToSearch) {var query = _tickets.Where((ticket, index) =>ticket.Numbers[0] == number1ToSearch|| ticket.Numbers[1] == number1ToSearch|| ticket.Numbers[2] == number1ToSearch|| ticket.Numbers[3] == number1ToSearch|| ticket.Numbers[4] == number1ToSearch|| ticket.Numbers[5] == number1ToSearch).Where((ticket, index) =>ticket.Numbers[0] == number2ToSearch|| ticket.Numbers[1] == number2ToSearch|| ticket.Numbers[2] == number2ToSearch|| ticket.Numbers[3] == number2ToSearch|| ticket.Numbers[4] == number2ToSearch|| ticket.Numbers[5] == number2ToSearch);}return query.Count();In the code, the bolded line demonstrates how the output of one method can serve as theinput for another method. This chaining of methods works because the list method returns otherlists. Thus, you could add multiple criteria by concatenating multiple Where() method calls.The methods are used to filter or manipulate the set where the details of the method areprovided by a lambda expression. Table 15-1 briefly describes some of the useful methods thatyou can use to filter and manipulate a list. The best way to learn about all of the methods is touse Visual C# Express, declare a list, and use IntelliSense to discover the different methodsavailable. Also, see http://msdn2.microsoft.com/en-us/vcsharp/aa336746.aspx for manyexamples that demonstrate the various list-manipulation methods.