Distinct in LINQ with anonymous types (in VB.NET)

Question

Supposing the referenced List below contains 2 elements:

Dim Countries = From c In List _
                Select New With { .Country = c.Country         


        

Answer 1

Distinct must know somehow which objects are the same. You select anonymus objects here, it doesn't know which are equal. I never wrote a single line of VB.Net, but I tried something, and it works:

Module Module1

    Sub Main()
        Dim countries As List(Of Country) = New List(Of Country)
        Dim spain1 As Country = New Country()
        Dim spain2 As Country = New Country()
        Dim spain3 As Country = New Country()
        Dim hungary As Country = New Country()
        spain1.ID = 1
        spain1.Name = "Spain"
        spain2.ID = 1
        spain2.Name = "Spain"
        spain3.ID = 2
        spain3.Name = "Spain"
        hungary.ID = 3
        hungary.Name = "Hungary"
        countries.Add(spain1)
        countries.Add(spain2)
        countries.Add(spain3)
        countries.Add(hungary)

        Dim ctr = From c In countries Select c.Name, c.ID
                  Distinct

        For Each c In ctr
            Console.WriteLine(c)
        Next
    End Sub

    Public Class Country

        Protected _name As String

        Protected _id As Long

        Public Property Name() As String
            Get
                Return _name
            End Get
            Set(ByVal value As String)
                _name = value
            End Set
        End Property

        Public Property ID() As Long
            Get
                Return _id
            End Get
            Set(ByVal value As Long)
                _id = value
            End Set
        End Property

    End Class
End Module

In your case:

Dim Countries = From c In List 
                Select c.Country, c.CountryID Distinct