Setting up a large number of aggregated values like sums, counts or averages can be a dreadful experience in the Pentaho Report Designer.
Calculations are performed by functions and expressions (let me call it just functions). These functions are added in the data tab of the report designer. Each function gets a name under which its result can be referenced. And then it needs to be configured properly. Usually, you have to set at least the field it should work on and the group on which it should reset.
Doing it for one field is not exciting, but ok. Doing it for 10 fields is no longer fun.
If you just want to print the result of that calculation, without ever using it as part of another computation, then here’s an easier way of aggregating data:
(1) Drag a number field onto your report and assign a field name to it (attribute common::fieldname).
(2) Set the aggregation you want to use via the attribute “wizard::aggregation-type”.
(3) Optional: Define the group on which you want to reset. If not defined, the current group is used.
This way of defining aggregations is used by the Report Design Wizard. To see a working example – just generate a report with it and add a summary on the fields.