In this sample, you can change the aggregate types for value fields using the dropdown list separately. The aggregate type can be set using the type property of the value field. The built-in aggregates are:
Sum, Average, Min, Max, Count, Distinct Count, Product,
Index, Population StDev, Sample StDev, Population Var, Sample Var, Running Totals,
Difference From, % of Difference From, % of Grand Total, % of Column Total, % of Row Total,
% of Parent Total, % of Parent Column Total, % of Parent Row Total.
To achieve aggregation through UI, navigate to "User Interaction > Field List" sample and click and open the value field settings menu to experience the same.