With DataGridView1
   .Columns.Add("Material", "Material")
   .Rows.Add("Eisen")
   .Rows.Add("Stahl")
   .Rows.Add("Eisen")
   .Rows.Add("Eisen")
   .Rows.Add("Alu")
   .Rows.Add("Eisen")
   .Rows.Add("Stahl")
   .Rows.Add("Eisen")
End With
 
Dim dic As New Dictionary(Of String, Integer), mat As String
 
With DataGridView1
   For rowindex As Integer = 0 To .Rows.Count - 1
       If .Rows(rowindex).Cells("Material").Value IsNot Nothing Then
          mat = .Rows(rowindex).Cells("Material").Value.ToString
          If dic.ContainsKey(mat) Then
             dic(mat) += 1
          Else
             dic.Add(mat, 1)
          End If
       End If
   Next rowindex
End With