linq concat column by val - vb.net

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))
};

Answer 2

Class Item
...
Public ReadOnly Property id As String
Get
Return col1 & "_" & col2 & "_" & col3
End Get
End Property
End Class
Dim groups = ItemList.GroupBy(Function(item) item.id)
Dim result = From g in groups
Select New Item(g(0).col1, g(0).col2, g(0).col3,
String.Join(" "c, g.Select(Function(i) i.description)))