Add Items to datatale per column instead of per row - vb.net

Question

Half a day of searching made at least my data readable in a datagrid in a wpf app.
My problem is (or what in think is my problem) would be the adding of data in the columns I created.
My source of data is from a dictionary of string, list(of string) with my dictionary key as the header and the List as it's items, also the dictionary and it's content has no fixed length.
And to display my data I used the combination of DataTable and DataGrid
Here's my snippet
Dim files As New Dictionary(Of String, List(Of String))
Dim dt As New DataTable
For Each item As KeyValuePair(Of String, List(Of String)) In files
dt.Columns.Add(item.Key)
For Each file As String In item.Value
Dim dr As DataRow = dt.NewRow
dr(dt.Columns(item.Key).Ordinal) = file
dt.Rows.Add(dr)
Next
Next
DGrid.ItemsSource = dt.AsDataView
It works(somewhat), but as you all have guessed all the succeeding displayed column items after the last one starts where it ended last(looks like a stair).
so the question is do I have to change the way I store my data(dictionary) or I am missing something and this can work as there is a way to add data per column instead of rows?
UPDATE
It's not pretty and I know there is a better solution out there.
What I did first was to just render/instantiate the table and it's content
Dim dt As New DataTable
For Each item As KeyValuePair(Of String, List(Of String)) In files
dt.Columns.Add(item.Key)
For Each file As String In item.Value
Dim dr As DataRow = dt.NewRow
dr(item.Key) = Nothing
dt.Rows.Add(dr)
Next
Next
Then edit it's content:
For Each item As KeyValuePair(Of String, List(Of String)) In files
For file_index As Integer = 0 To item.Value.Count - 1
dt.Rows(file_index)(item.Key) = item.Value(file_index)
Next
Next
This is a bad solution but it works. Is there a better way?

Answer 1

you need to reuse existing rows for this. And add new one only when you have more items then rows.
Dim Files As New Dictionary(Of String, List(Of String))
Dim T As New DataTable, R As DataRow
For Each Pair As KeyValuePair(Of String, List(Of String)) In Files
T.Columns.Add(Pair.Key)
For i As Integer = 0 To Pair.Value.Count - 1
If i < T.Rows.Count Then
R = T.Rows(i)
Else
R = T.NewRow()
T.Rows.Add(R)
End If
R(Pair.Key) = Pair.Value(i)
Next
Next