# Package org.eclipse.viatra.query.runtime.rete.aggregation

- Interface Summary
  Interface | Description
  --- | ---
  IAggregatorNode | Expresses that aggregators expose specialized non-enumerable indexers for outer joining.

- Class Summary
  Class | Description
  --- | ---
  AbstractColumnAggregatorNode<Domain,​Accumulator,​AggregateResult> | Groups incoming tuples by the given mask, and aggregates values at a specific index in each group.
  AbstractColumnAggregatorNode.NetworkStructureChangeSensitiveLogic |
  ColumnAggregatorNode<Domain,​Accumulator,​AggregateResult> | Timeless implementation of the column aggregator node.
  CountNode | An aggregation node that simply counts the number of tuples conforming to the signature.
  GroupedMap<GroupedKeyType,​ValueType> | An optimized `Map` implementation where each key is produced by joining together a group tuple and some other object (via left inheritance).
  GroupedSet<GroupingValueType,​GroupedKeyType,​WholeKeyType> | An optimized `Set` implementation where each contained value is produced by combining together a grouping value and some other (key) object.
  IndexerBasedAggregatorNode | A special node depending on a projection indexer to aggregate tuple groups with the same projection.