Module Module1

    Public Class Company
        Public Property Name As String
    End Class

    Public Enum Format
        Style1
        Style2
        Style3
    End Enum

    Public Class Definition
        Public Property ID As Integer
        Public Property Company As Company
        Public Property Format As Format
    End Class

    Sub Main()

        Dim defs As New List(Of Definition)()
        defs.Add(New Definition() With {.ID = 1, .Company = Nothing, .Format = Format.Style1})
        defs.Add(New Definition() With {.ID = 2, .Company = Nothing, .Format = Format.Style2})
        defs.Add(New Definition() With {.ID = 3, .Company = Nothing, .Format = Format.Style3})

        defs.Add(New Definition() With {.ID = 4, .Company = Nothing, .Format = Format.Style1}) '-- <<< WILDCARD 1
        defs.Add(New Definition() With {.ID = 4, .Company = New Company() With {.Name = "Test"}, .Format = Format.Style1}) '-- <<< WILDCARD 2

        '-- Get groups
        Dim byFormat = From d In defs
                       Group d By KeyedFormat = New With {Key .Format = d.Format, Key .Company = d.Company} Into Group
                       Select New With
                              {
                                  .Company = KeyedFormat.Company,
                                  .Format = KeyedFormat.Format,
                                  .Definitions = Group.OrderByDescending(Function(x) x.ID)
                              }

    End Sub

End Module