Public Class Form1
  Dim dt1 As New DataTable
  Dim dt2 As New DataTable
 
  Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) _
      Handles MyBase.Load
 
    dt1Erstellen()
    dt2Erstellen()
 
    DataGridView1.DataSource = dt2
 
    Dim dr As DataRow
 
    For Each dr In dt1.Rows
      SetDTValue(dr!Nachname, dr!Wochentag)
    Next
 
  End Sub
 
  Private Sub dt1Erstellen()
    dt1.Columns.Add("Nachname")
    dt1.Columns.Add("Notes")
    dt1.Columns.Add("Wochentag")
 
    dt1.Rows.Add("Meyer", "Hof fegen", "Montag")
    dt1.Rows.Add("Müller", "Kühe melken", "Dienstag")
    dt1.Rows.Add("Meyer", "Kühe melken", "Dienstag")
    dt1.Rows.Add("Müller", "Kühe melken", "Dienstag")
    dt1.Rows.Add("Schmidt", "Trecker tanken", "Mittwoch")
    dt1.Rows.Add("Hinz", "Bäuerin melken", "Donnerstag")
    dt1.Rows.Add("Kunz", "Heu ernten", "Freitag")
 
  End Sub
 
  Private Sub dt2Erstellen()
    dt2.Columns.Add("Montag")
    dt2.Columns.Add("Dienstag")
    dt2.Columns.Add("Mittwoch")
    dt2.Columns.Add("Donnerstag")
    dt2.Columns.Add("Freitag")
  End Sub
 
  Private Sub SetDTValue(ByVal Nachname As String, ByVal Wochentag As _
      String)
    Dim row As DataRow = GetRowForInsert(Wochentag)
    Dim newRow As Boolean = row Is Nothing
    If newRow Then row = dt2.NewRow()
    row(Wochentag) = Nachname
    If newRow Then dt2.Rows.Add(row)
  End Sub
 
  Private Function GetRowForInsert(Wochentag As String) As DataRow
    For Each r As DataRow In dt2.Rows
      If IsDBNull(r(Wochentag)) Then Return r
    Next
    Return Nothing
  End Function
End Class

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Jeder, der behauptet das gesamte .NET-Framework zu kennen ist entweder verrückt oder Sheldon Cooper