dataset add colum and remove and clone and copy

DataTable GetTable()
    {
        //
        // Here we create a DataTable with four columns.
        //
        DataTable table = new DataTable();
        table.Columns.Add("Dosage", typeof(int));
        table.Columns.Add("Drug", typeof(string));
        table.Columns.Add("Patient", typeof(string));
        table.Columns.Add("Date", typeof(DateTime));

        //
        // Here we add five DataRows.
        //
        table.Rows.Add(25, "Indocin", "David", DateTime.Now);
        table.Rows.Add(50, "Enebrel", "Sam", DateTime.Now);
        table.Rows.Add(10, "Hydralazine", "Christoff", DateTime.Now);
        table.Rows.Add(21, "Combivent", "Janet", DateTime.Now);
        table.Rows.Add(100, "Dilantin", "Melanie", DateTime.Now);
        return table;
    }
    protected void Page_Load(object sender, EventArgs e)
    {

        DataTable ds = new DataTable();
        ds = GetTable();
        DataSet ds1 = new DataSet();
        ds1.Tables.Add(ds);
        _FilterAndInsert(ds1);
        //ds.Tables.Add(employees);
        //ds.Tables.Add(payCheckes);
    }
    private void _FilterAndInsert(DataSet sourceSet)
    {
         sourceSet.Tables[0].Columns.Add("ppID", typeof(string));
        ///Apply your filter clauses in Select() function parameter
        DataRow[] rows = sourceSet.Tables[0].Select("Dosage >="+25+"");
        ///Get the structure of source table
        DataTable tempTable = sourceSet.Tables[0].Clone();
        ///Add the filtered rows in temp table
        int i = 0;
        foreach (DataRow row in rows)
        {
            tempTable.Rows.Add(row.ItemArray[0], row.ItemArray[1], row.ItemArray[2], row.ItemArray[3], row.ItemArray[4] = (i+1).ToString());
            i++;
        }
        tempTable.Columns.Remove("Date"); 
        tempTable.AcceptChanges();
        ///Create new dataset
        DataSet resultSet = new DataSet();
        ///Add temp table at first index or modify this code sequence as you require
        resultSet.Tables.Add(tempTable);
        for (int index = 1; index < sourceSet.Tables.Count; index++)
        {
            ///Set the copy of source table in local instance
            DataTable tableToAdd = sourceSet.Tables[index].Copy();
            ///Remove from source to avoid any exceptions
            sourceSet.Tables.RemoveAt(index);
            ///Add the copy to result set
            resultSet.Tables.Add(tableToAdd);
        }
        ///Set the copy to source table from result set
        sourceSet = resultSet.Copy();

        //DataTable tbl;
        //DataTable tbl2 = new DataTable();
        //DataSet ds = new DataSet();
        //ds.Tables.Add(new DataTable());
        //ds.Tables[0].Columns.Add("ID", typeof(int));
        //ds.Tables[0].Columns.Add("Tour_Code", typeof(int));
        //ds.Tables[0].Columns.Add("Tour_Date", typeof(string));
        ////ds.Tables[0].Columns.Add("No_Of_Vehicle", typeof(int));
        //ds.Tables[0].Columns.Add("Vehicle", typeof(string));
        //tbl2 = ds.Tables[0].Clone();
    }