| Class | Description | 
|---|---|
| Aggregator<IN,BUF,OUT> | 
 A base class for user-defined aggregations, which can be used in  
Dataset operations to take
 all of the elements of a group and reduce them to a single value. | 
| MutableAggregationBuffer | 
 A  
Row representing 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. 
 |