static void UngroupFieldItems(IWorkbook workbook)
        {
            #region #UngroupFieldItems
            Worksheet worksheet = workbook.Worksheets["Report8"];
            workbook.Worksheets.ActiveWorksheet = worksheet;

            // Access the pivot table by its name in the collection.
            PivotTable pivotTable = worksheet.PivotTables["PivotTable1"];
            // Access the "DATE" field by its name in the collection.
            PivotField field = pivotTable.Fields["DATE"];
            // Group field items by days.
            field.GroupItems(field.GroupingInfo.DefaultStartValue, field.GroupingInfo.DefaultEndValue, 50, PivotFieldGroupByType.Days);
            // Ungroup field items.
            field.UngroupItems();
            #endregion #UngroupFieldItems
        }
        static void UngroupSpecificItem(IWorkbook workbook)
        {
            #region #UngroupSpecificItem
            Worksheet worksheet = workbook.Worksheets["Report11"];
            workbook.Worksheets.ActiveWorksheet = worksheet;

            // Access the pivot table by its name in the collection
            PivotTable pivotTable = worksheet.PivotTables["PivotTable1"];
            // Access the "State" field by its name in the collection.
            PivotField field = pivotTable.Fields["State"];
            // Add the "State" field to the column axis area.
            pivotTable.ColumnFields.Add(field);

            // Group the first three items in the field.
            IEnumerable <int> items = new List <int>()
            {
                0, 1, 2
            };
            field.GroupItems(items);
            // Access the created grouped field by its index in the field collection.
            int        groupedFieldIndex = pivotTable.Fields.Count - 1;
            PivotField groupedField      = pivotTable.Fields[groupedFieldIndex];
            // Set the grouped item caption to "West".
            groupedField.Items[0].Caption = "West";

            // Group the remaining field items.
            items = new List <int>()
            {
                3, 4, 5
            };
            field.GroupItems(items);
            // Set the grouped item caption to "Midwest"
            groupedField.Items[1].Caption = "Midwest";

            // Ungroup the "West" item.
            items = new List <int> {
                0
            };
            groupedField.UngroupItems(items);
            #endregion #UngroupSpecificItem
        }