This Operator can be used to combine sequent elements, e.g. by a set of grouping attributes or with a predicates.
Warning: This operator ignores timestamps, so the result may not be valid regarding temporal correctness! If you want to garantee temporal correctness use Window operator and Aggregate (and Group) operator
In the attributes case, the elements are merged with also given aggregations functions, as long as the grouping attributes (e.g. a sensorid) are the same. When a new group is opened (e.g. a measurement from a new sensor) the old aggregates values and the grouping attributes are created as a result.
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