Excluding data sets
If you want to only analyze selected data sets, you can do so. Don't exclude all the other points. And don't expect your selection of data sets to matter when you click the Analyze dialog. Instead, you choose which data sets to analyze on the right side of the Analyze dialog. You can change your mind later via Change..Data analyzed.
Empty data sets
How does Prism deal with empty data sets (or data sets with all values excluded) when analyzing data. If you selected to analyze all the data sets (the default), then Prism leaves empty data sets in results if there are empty data sets in the data table. That way the data set letter is always the same for data tables and results. In other words, the results for data set E are always in results data set E. But if you selected to only analyze selected data sets, Prism only analyzes selected data sets that are not empty. If you choose to analyze data sets C, D and E, but data set D is empty, then the results for data set C will appear in column A of the results table, and the results for data set E will appear in column B in the results table.
Excluding a range of rows
Prism is set up to work with sets of data set columns. There is no way to select a range of rows to analyze. The workaround would be to duplicate the table, and then remove unwanted rows from the copy.