Question

I just looking how to use LINQ for grouping a list.

Class Item
    Public col1 As String
    Public col2 As String
    Public col3 As String
    Public description As String
    Public Sub New(ByVal col1 As String, ByVal col2 As String, 
                   ByVal col3 As String, ByVal description As String)
        Me.col1 = col1
        Me.col2 = col2
        Me.col3 = col3
        Me.description = description
    End Sub
End Class  


    Dim ItemList As New List(Of Item)
    ItemList.Add(New Item("A", "A", "A", "1"))
    ItemList.Add(New Item("A", "A", "A", "2"))
    ItemList.Add(New Item("A", "B", "A", "3"))
    ItemList.Add(New Item("A", "B", "A", "4"))
    ItemList.Add(New Item("A", "B", "B", "5"))
    ItemList.Add(New Item("A", "B", "C", "6"))

Result should be list of 4 items:

    '[0] = "A", "A", "A", "1 2"
    '[1] = "A", "B", "A", "3 4"
    '[2] = "A", "B", "B", "5"
    '[3] = "A", "B", "C", "6"

Answer 1

If I understand your requirement to group by the 3 columns and join their descriptions, the following LINQ statement should work:

var query = from item in ItemList
            group item by
                new { Col1 = item.col1, Col2 = item.col2, Col3 = item.col3 }
            into g
            select new
            {
                 Col1 = g.Key.Col1,
                 Col2 = g.Key.Col2,
                 Col3 = g.Key.Col3,
                 Description = String.Join(" ", g.Select(xx => xx.description))
            };