Github user aljoscha commented on a diff in the pull request: https://github.com/apache/flink/pull/466#discussion_r26105155 --- Diff: flink-java/src/main/java/org/apache/flink/api/java/operators/UnsortedGrouping.java --- @@ -159,7 +159,23 @@ public UnsortedGrouping(DataSet<T> set, Keys<T> keys) { return new GroupReduceOperator<T, R>(this, resultType, dataSet.clean(reducer), Utils.getCallLocationName()); } - + + /** + * Applies a partial GroupReduce transformation on a grouped {@link DataSet}. + * In contrast to the reduceGroup transformation, the GroupReduce function is only called on each partition. Thus, + * partial solutions are likely to occur. + * @param reducer The ReduceFunction that is applied on the DataSet. + * @return A GroupReducePartial operator which represents the partially reduced DataSet + */ + public <R> GroupReducePartialOperator<T, R> reduceGroupPartially(GroupReduceFunction<T, R> reducer) { + if (reducer == null) { + throw new NullPointerException("GroupReduce function must not be null."); + } + TypeInformation<R> resultType = TypeExtractor.getGroupReduceReturnTypes(reducer, this.getDataSet().getType()); + + return new GroupReducePartialOperator<T, R>(this, resultType, dataSet.clean(reducer), Utils.getCallLocationName()); + } + --- End diff -- Why do we have this here. Partial GroupReduce doesn't make sense on a grouping. Thats's what a regular GroupReduce is. Or am I missing something?
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