' Visual Basic 2008 9.0 .NET Examples - Query Methods - New in Visual Basic 2008 - 9.0 : 
Option Strict On
Option Infer On
Public Class Counter
    Private m_Value As Integer
    Public Property Value() As Integer
        Get
            Value = m_Value
        End Get
        Set(ByVal value As Integer)
            m_Value = value
        End Set
    End Property
End Class
Public Module MyEnumerable
    <System.Runtime.CompilerServices.Extension()> _
    Public Function GetWhere(Of T)(ByVal source As IEnumerable(Of T), _
                                   ByVal predicate As Func(Of T, Boolean)) _
                                                            As IEnumerable(Of T)
        Dim getWhereList As New List(Of T)
        For Each item As T In source
            If predicate.Invoke(item) Then
                getWhereList.Add(item)
            End If
        Next
        GetWhere = getWhereList
    End Function
End Module
Public Class Example1
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        Dim predicate As Func(Of Counter, Boolean) = _
                                            Function(counter) counter.Value > 15
        Dim query1 = MyEnumerable.GetWhere(source, predicate)              ' (1)
        For Each counter As Counter In query1
            Console.WriteLine(counter.Value)
        Next
        Console.WriteLine()
        '
        Dim query2 = source.GetWhere(Function(counter) counter.Value < 25) ' (2)
        For Each counter As Counter In query2
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example2
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        Dim predicate As Func(Of Counter, Boolean) = _
                                            Function(counter) counter.Value > 15
        Dim query1 = System.Linq.Enumerable.Where(source, predicate)
        For Each counter As Counter In query1
            Console.WriteLine(counter.Value)
        Next
        Console.WriteLine()
        '
        Dim query2 = source.Where(Function(counter) counter.Value < 25)
        For Each counter As Counter In query2
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example3
    Public Shared Sub Main()
        Dim source1 = New Object() {1, "two", "3"c, "four", 5.0}
        Dim words As IEnumerable(Of String) = source1.OfType(Of String)()
        For Each word As String In words
            Console.WriteLine(word)
        Next
        Console.WriteLine()
        '
        Dim source2 As New ArrayList
        source2.Add(New Counter With {.Value = 10})
        source2.Add(New Counter With {.Value = 20})
        source2.Add(New Counter With {.Value = 30})
        Dim counters As IEnumerable(Of Counter) = source2.OfType(Of Counter)()
        For Each counter As Counter In counters
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example4
    Public Shared Sub Main()
        Dim source = New Object() {1, "two", "3"c, "four", 5.0}
        Dim predicate1 As Func(Of String, Boolean) = _
                                               Function(text) text.Contains("o")
        Dim predicate2 As Func(Of String, Boolean) = _
                                             Function(text) text.StartsWith("f")
        Dim words As IEnumerable(Of String)
        words = source.OfType(Of String).Where(predicate1).Where(predicate2)
        For Each word As String In words
            Console.WriteLine(word)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example5
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        Dim query = source.Where(Function(counter) True)
        '
        For Each counter As Counter In query                               ' (1)
            Console.WriteLine(counter.Value)
        Next
        Console.WriteLine()
        '
        source(1) = New Counter With {.Value = 200}
        '
        For Each counter As Counter In query                               ' (2)
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example6
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        Dim query = source.GetWhere(Function(counter) True)
        '
        For Each counter As Counter In query                               ' (1)
            Console.WriteLine(counter.Value)
        Next
        Console.WriteLine()
        '
        source(1) = New Counter With {.Value = 200}
        '
        For Each counter As Counter In query                               ' (2)
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example8
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        Dim query = source.Where(Function(counter) True)
        '
        Dim queryArray As Counter() = query.ToArray()
        Dim queryList As List(Of Counter) = query.ToList()
        '
        source(1) = New Counter With {.Value = 200}
        '
        For Each counter As Counter In queryArray                          ' (1)
            Console.WriteLine(counter.Value)
        Next
        Console.WriteLine()
        '
        For Each counter As Counter In queryList                           ' (2)
            Console.WriteLine(counter.Value)
        Next
        '
        Console.ReadLine()
    End Sub
End Class
Public Class Example9
    Public Shared Sub Main()
        Dim source = New Counter() {New Counter With {.Value = 10}, _
                                    New Counter With {.Value = 20}, _
                                    New Counter With {.Value = 30}}
        '
        Console.WriteLine(source.Any())
        Console.WriteLine(source.All(Function(counter) counter.Value Mod 2 = 0))
        Console.WriteLine(source.Average(Function(counter) counter.Value))
        Console.WriteLine(source.ElementAt(2).Value)
        Console.WriteLine(source.First().Value)
        '
        Console.ReadLine()
    End Sub
End Class

' Visit www.studyvb.com for more examples.  Copyright 2003-2008 De Wolf.