Group-By Processing

From Fmepedia

Group-By Processing is the use of Group-Based Processing in such a way to process features within a number of user-defined groups rather than as a single group of all features. The usual method is to apply a Group-By option within a Group-Based Transformer.

A Group-By option allows you to select one or more attributes. Features which have all of the selected attributes in common are considered to be part of the same group. Note that in many cases, the values of the attributes that were not selected are removed.