Organizing data in groups
As the previous section describes, sorting data makes a report more readable and useful. Sorting, however, is only one of the ways to organize data in a report. It is common for reports to present data that is organized into meaningful groups, especially reports that contain large amounts of data.
Consider the task of listing every item a corporation owns, along with information such as the category, purchase price, purchase date, inventory code, location, and supplier. If a report presents all these items in an unorganized list or even in a sorted list, there is no way to determine how much the corporation has spent, for example, on office furniture or computer hardware, because this information cannot be calculated. The report cannot help you see which year had the most purchases, nor is it easy to tell which items are located in a field office and which items are in the warehouse.
To organize this information into a useful inventory report, you create data groups. Data groups contain related data rows. For example, you can create a report that lists items by category—all office furniture in one group, all computer hardware in another group, all computer software in a third group, and so on. For each group, you can calculate aggregate data, such as the total purchase price or the count of items in a group. Organizing data in groups makes it easier to compare and analyze information.
Compare the reports in Figure 4-6 and Figure 4-7. The report design in Figure 4-6 displays sales information in a simple list. The data rows are sorted by sales office, then by product line. Notice the repeated sales office name and product lines.
Figure 4-6  
Figure 4-7  
The report design in Figure 4-7 shows the same data. Unlike the report design in Figure 4-6, this design groups the rows by sales office then by product line. Data appears in a hierarchy. The report design does not contain repeated values for office names and product lines. In addition, totals, displayed in italics, appear at the end of each product line and sales office group.
As the example reports Figure 4-6 and Figure 4-7 show, a report design that groups data provides a more effective way to view data. When you group data, you can:
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In addition, BIRT Studio completes the following actions when you group data:
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