The 'jfr view' command groups data according to a key, and for every key, a new Function object needs to be created. This is done in a factory method, where the aggregator function is selected based on the type of field.

Instead of performing this selection for each key, a factory could be used. This approach would also simplify the implementation of JDK-8366480 (Context expanded column), where a new Function may be needed for every event.