| Class | Description | 
|---|---|
| Aggregator<IN,BUF,OUT> | A base class for user-defined aggregations, which can be used in  Datasetoperations to take
 all of the elements of a group and reduce them to a single value. | 
| MutableAggregationBuffer | A  Rowrepresenting a mutable aggregation buffer. | 
| UserDefinedAggregateFunction | Deprecated UserDefinedAggregateFunction is deprecated. | 
| UserDefinedFunction | A user-defined function. | 
| Window | Utility functions for defining window in DataFrames. | 
| WindowSpec | A window specification that defines the partitioning, ordering, and frame boundaries. |