Add Excel's grouping and outlining functionality to a workbook with ExcelWriter to display nested data.

        private ExcelApplication xlw;
        private Workbook wb;
        private Worksheet ws;
        private int year = 2008;
        private bool bCollapsed = true;

        /// <summary>
        /// Build the report with ExcelApplication
        /// </summary>
        public void GenerateReport()
        {
            // Creat a blank workbook and a single worksheet //
            xlw = new ExcelApplication();
            wb = xlw.Create(ExcelApplication.FileFormat.Xlsx);
            ws = wb.Worksheets[0];

            // Populate //
            this.PopulateWorksheet(year);

            //TODO Not implemented
            //ws.createRangeOfColumns  

            // Save the report //
            xlw.Save(wb, @"..\..\Output\GroupingSubtotals_output.xlsx");
        }

        /// <summary>
        /// Write values and import data into the  Worksheet. 
        /// Also, sets up outlining and formulas.
        /// </summary>
        /// <param name="year">Display orders from this year</param> 
        /// <param name="bCollapsed">Show outlines as collapsed?</param>
        /// <param name="bAddChart">Add chart to worksheet?</param>
        private void PopulateWorksheet(int year)
        {
            // Create a style for the total rows.
             // Make the font bold-faced, and shade
             // the cells with light grey.
            GlobalStyle totalStyle = wb.CreateStyle();
            totalStyle.Font.Bold = true;
            totalStyle.BackgroundColor = wb.Palette.GetClosestColor(211, 211, 211);

            // This area will be used to determine how
             // many rows of data were imported from the DataTable
            Area area = null;

            // These row and col variables are counters to
             // keep track of the current row and column
            int row = 0;
            int col = 0;

            // Cell references for the total rows will be
             // added into these vectors for the later use in
             // a chart
            ArrayList categoryList = new ArrayList();
            ArrayList seriesList = new ArrayList();

            string[] categories = { "Bike", "Component", "Clothing", "Accessory" };

            // Loop through the DataTables returned
             // from the getData method
            for (int i = 0; i < 4; i++)
            {
                Cell c = ws[row, col];

                // Write the category name //
                c.Value = categories[i];

                // Add the category cell to the category vector //
                categoryList.Add(String.Format("{0}!{1}", ws.Name, ws[row, col].Name));

                ws[row, col + 1].Value = "Total:";

                // Apply totalStyle to the Area, 
                 // and create a border around the row.
                Area totalArea = ws.CreateArea(row, col, 1, 3);
                totalArea.SetStyle(totalStyle);
                ws[row, col + 1].Style.HorizontalAlignment = Style.HAlign.Right;
                totalArea.BorderAround.Style = Border.LineStyle.Thin;

                DataImportProperties dProps = wb.CreateDataImportProperties();
                dProps.ConvertStrings = true;
                dProps.Truncate = true;

                // Import the data from the DataTable //
                DataTable dt = GetData(i + 1);
                area = ws.ImportData(dt, ws[row + 1, 1], dProps);

                // Compute where the last row of data was imported to //
                int lastRow = row + area.RowCount + 1;

                // Loop through all rows that were just imported
                 // and set the outline level to group the rows.
                for (int iRow = row + 1; iRow < lastRow; iRow++)
                {
                    RowProperties rp = ws.GetRowProperties(iRow);
                    rp.OutlineCollapsed = bCollapsed;
                    rp.OutlineLevel = 1;
                }

                // Add a SUBTOTAL formula to the total row. //
                string formula = String.Format("=SUBTOTAL(9,{0}:{1})", ws[row + 1, 2].Name, ws[lastRow, 2].Name);
                ws[row, 2].Formula = formula;

                // Add the total cell reference to the series vector //
                seriesList.Add(String.Format("{0}!{1}", ws.Name, ws[row, 2].Name));

                // Increment the row counter to the end of the 
                 // imported data area, and skip two.
                row = row + area.RowCount + 2;
            }

            // TODO Not implemented
            //ws.createRange("A1:C1").autoFitWidth();

            // Set column widths //
            ws.GetColumnProperties(0).Width = 80;
            ws.GetColumnProperties(1).Width = 195;
            ws.GetColumnProperties(2).Width = 110;

            // Create a style to format the currency column //
            GlobalStyle stylCurrency = wb.CreateStyle();

            // Create and apply a typical Accounting format
             // to the currency column.
             //
            NumberFormat nf = wb.NumberFormat;
            String fmtString = nf.CreateAccounting(2, true, null);
            stylCurrency.NumberFormat = fmtString;
            Area ar = ws.CreateArea(0, 2, row - 1, 1);
            ar.ApplyStyle(stylCurrency);

            // Join the cell reference vectors into formula 
             // strings for the charts.
            string categoryFormula = String.Join(",", (string[])categoryList.ToArray(typeof(string)));
            string seriesFormula = String.Join(",", (string[])seriesList.ToArray(typeof(string)));
            Console.WriteLine(categoryFormula);
            // Create a 3D pie chart on a chartsheet //

            Chartsheet wsChart =
                wb.Worksheets.CreateChartsheet(ChartType.Pie.Pie3D, "Chart");
            Chart chrt = wsChart.Chart;
            chrt.SeriesCollection.CategoryData = categoryFormula;

            Series srsSales = chrt.SeriesCollection.CreateSeries(seriesFormula);
        }
            
        ///<summary>
        /// Uses a 3rd party generic CSV parser
        /// DataTable of product line items
        /// </summary>
        /// <returns></returns>
        private DataTable GetData(int catId)
        {
            DataTable dt=new DataTable();
            if (catId==1)
                dt = GetCSVData(@"..\..\Data\GroupingBikes.csv");
            if (catId==2)
                dt = GetCSVData(@"..\..\Data\GroupingClothing.csv");
            if (catId==3)
                dt = GetCSVData(@"..\..\Data\GroupingClothing.csv");
            if (catId==4)
                dt = GetCSVData(@"..\..\Data\GroupingAccessories.csv");
            return dt;
        }

        //Uses CSV reader
        System.Data.DataTable GetCSVData(string csvFileName)
        {
            DataTable dt;
            using (GenericParserAdapter parser = new GenericParserAdapter(csvFileName))
            {
                parser.ColumnDelimiter = ',';
                parser.FirstRowHasHeader = true;

                dt = parser.GetDataTable();
            }
            return dt;
        }