DataTable testtable = new DataTable();
      testtable.Columns.Add("ID");
      testtable.Columns.Add("ProductName");

      testtable.Rows.Add("1", "1");
      testtable.Rows.Add("1", "1");
      testtable.Rows.Add("1", "1");
      testtable.Rows.Add("2", "2");
      testtable.Rows.Add("3", "3");
      DataTable finalltable = new DataTable();
      finalltable = testtable.Clone();
      finalltable.Clear();
      
      var rows = from row in testtable.AsEnumerable() group row by row["ID"] into myrow select myrow.FirstOrDefault();
      foreach (DataRow row in rows)
      {
        finalltable.ImportRow(row);
      }

testtable = testtable.DefaultView.ToTable(true, new string[] { "ID", "ProductName" });