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CH AP T E R 1 5 ■ L E A R N I N G A B OU T L I N Q 405
■Note LINQ’s strength is in its ability to slice and dice data to find the information that you want （which is
easy because it is data source–agnostic）。 LINQ requires more resources than similar Visual Basic code in
longhand format。 But the benefit you get with LINQ is reusable code that you can maintain。
In the preceding section； we used LINQ to solve the frequency problem in a manner that
promoted reusability。 For example； if you wanted to find out more statistics of the lottery draws； all
you would need to do is write more LINQ statements that sliced and diced the existing list
of lottery draws。 It would require adding only the method calls to the IExtendedProcessor。
Destroy（） method。 However； let’s consider the problem solved and think about what else can
be done with LINQ。
Learning More LINQ Tricks
LINQ is not the only way to filter data。 Associated with LINQ are a number of extension methods
that can be applied to lists。 For example； to filter for the frequency of a particular number； the
following code could also have been used。
Function FrequencyOfANumber（ByVal numberToSearch As Integer） As Integer
Dim query = _tickets。Where（ _
Function（ticket； index） _
ticket。Numbers（0） = numberToSearch _
Or ticket。Numbers（1） = numberToSearch _
Or ticket。Numbers（2） = numberToSearch _
Or ticket。Numbers（3） = numberToSearch _
Or ticket。Numbers（4） = numberToSearch _
Or ticket。Numbers（5） = numberToSearch）
Return query。Count（）
End Function
The ideas of LINQ that include From； Where； and Select are not lost； they just have not been
used。 The From part is the _tickets variable itself。 The Where part is the method Where（）； and the
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 parame
ters： the object and the index of the object。 The lambda expression expects that you return a
Boolean value indicating whether the ticket item should be added to a returned list。
LINQ is a syntax that wraps SQL…like text。 LINQ is much easier to understand and program
than using the method…call syntax of the previous example。 Using the methods gives you more
flexibility； but they also are more plicated to write。
For example； if you wanted to find the frequency of two numbers in a list； you could use
this code：
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406 CH AP T E R 1 5 ■ L E A R N I N G A B OU T L I N Q
Function FrequencyOfTwoNumbersList（ByVal number1ToSearch As Integer ； _
ByVal number2ToSearch As Integer） As Integer
Dim query = _tickets。Where（ _
Function（ticket； index） _
ticket。Numbers（0） = number1ToSearch _
Or ticket。Numbers（1） = number1ToSearch _
Or ticket。Numbers（2） = number1ToSearch _
Or ticket。Numbers（3） = number1ToSearch _
Or ticket。Numbers（4） = number1ToSearch _
Or ticket。Numbers（5） = number1ToSearch）。Where（ _
Function（ticket； index） _
ticket。Numbers（0） = number2ToSearch _
Or ticket。Numbers（1） = number2ToSearch _
Or ticket。Numbers（2） = number2ToSearch _
Or ticket。Numbers（3） = number2ToSearch _
Or ticket。Numbers（4） = number2ToSearch _
Or ticket。Numbers（5） = number2ToSearch）
Return query。Count（）
End Function
In the code； the bolded line demonstrates how the output of one method can serve as the
input for another method。 This chaining of methods works because the list method returns
other lists。 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 are
provided by a lambda expression。 Table 15…1 briefly describes some of the useful methods that
you can use to filter and manipulate a list。 The best way to learn about all of the methods is to
use Visual Basic Express； declare a list； and use IntelliSense to discover the different methods
available。 Also； see http：//msdn2。microsoft。/en…us/vbasic/bb688088。aspx for many exam
ples that demonstrate the various list…manipulation methods。
Table 15…1。 Some Methods for Filtering and Manipulating Lists
Method Description
Aggregate（） Returns a fact about the list。 A fact could be how many even numbers there are
or the frequency of a particular number。 All of the elements in the list are iterated
and returned as a single fact； not as a list。
All（） Iterates all elements of the list and tests according to a lambda expression；
where a True or False is returned。 For example； the test could be to find out if all
objects have a value greater than 10。 The test needs to return only a True or
False value for the individual object； where the All（） method will correlate the