aTicket。Numbers（2） = numberToSearch OrElse _ aTicket。Numbers（3） = numberToSearch OrElse _ aTicket。Numbers（4） = numberToSearch OrElse _ aTicket。Numbers（5） = numberToSearch Then runningTotal ＋= 1 End If Next Return runningTotal End Function Notice the similarity of the code to the code presented in Chapter 9。 The problem with this code is that you are iterating and solving a particular problem。 The code cannot be easily adapted to solving another problem。 The reusable code is in the form of a LINQ expression： Private Function FrequencyOfANumber（ByVal numberToSearch As Integer） As Integer Dim query = From ticket In _tickets _ Where 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 _ Select ticket。Numbers Return query。Count（） End Function The LINQ expression uses many constructs similar to a SQL SELECT statement。 Here are the basic rules of LINQ： o All LINQ queries must have a data source （From）。 o All LINQ queries must have a filter （Where）； however； if the filter does not exist； an auto matic include…everything filter is implied。 o All LINQ queries must have a resulting dataset creator （Select）。 To execute a LINQ expression； you need a data source。 The data source could be an object list； an XML document； or even a relational database table。 In the example； the data source is an object list and is defined using the From statement： From ticket In _tickets …………………………………………………………Page 426…………………………………………………………… 404 CH AP T E R 1 5 ■ L E A R N I N G A B OU T L I N Q Looking at the From statement； you could get the idea that it is a For Each statement without the types。 Indeed； the iteration happens only when you actually try to use the result of the LINQ query。 The From statement is saying to iterate the data source and assign each element （a Ticket） to the variable ticket。 Note； however； that there is no explicit type information； which is one of the strengths of LINQ—you have the ability to easily slice and dice data to suit your needs。 As you retrieve each item； you want to verify whether the item matches your needs。 If you look at the code that isn’t reusable； you’ll see that it checks this with an If statement。 In LINQ； you use the Where statement； which is similar to its SQL equivalent。 With the Where statement； you test to see if the item matches your criteria。 In our case； we check each number in the Ticket instance to see if it matches the number we’re currently seeking。 If the Where returns True； we have a match and we will want to do something。 In the code that isn’t reusable； that means incrementing the runningTotal integer。 In LINQ； the aim is to filter the data source （_tickets in our case）； and thus the Select statement is used to create a new result set of drawn numbers。 This result set contains all of the draws with the number we’re looking for （numberToSearch）； and if the draws are counted； we can get the frequency of that number； which we then return。 Let’s look at the LINQ that could be used to find the frequency of two numbers being drawn。 Function FrequencyOfTwoNumbers（ByVal number1ToSearch As Integer； _ ByVal number2ToSearch As Integer） As Integer Dim query = From ticket2 In _ （From ticket In _tickets _ Where 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 _ Select ticket） _ Where ticket2。Numbers（0） = number2ToSearch _ Or ticket2。Numbers（1） = number2ToSearch _ Or ticket2。Numbers（2） = number2ToSearch _ Or ticket2。Numbers（3） = number2ToSearch _ Or ticket2。Numbers（4） = number2ToSearch _ Or ticket2。Numbers（5） = number2ToSearch _ Select ticket2。Numbers Return query。Count（） End Function The LINQ statement is a concatenation of two LINQ queries； where one LINQ query is bolded。 When the query is executed； the embedded query is executed and generates a result set。 The result set is a data source on which the outer and second query operates； which then generates another result set。 You do not need to embed LINQ queries as in the preceding code。 You could write functions and embed the result of a LINQ query as the data source of another LINQ query。 The power of LINQ is that you can； in theory； arbitrarily embed many queries within other queries； since you are creating a filtering mechanism where one result set is the data source of another query。 …………………………………………………………Page 427……………………………………………………………