Github user mxm commented on a diff in the pull request:
https://github.com/apache/flink/pull/466#discussion_r26120661
--- Diff:
flink-java/src/main/java/org/apache/flink/api/java/operators/SortedGrouping.java
---
@@ -156,6 +156,23 @@ public SortedGrouping(DataSet<T> set, Keys<T> keys,
String field, Order order) {
return new GroupReduceOperator<T, R>(this, resultType,
dataSet.clean(reducer), Utils.getCallLocationName() );
}
+ /**
+ * Applies a partial GroupReduce transformation on a grouped and sorted
{@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 --
We need a grouping to combine the correct values, don't we? Otherwise, we
would perform an AllReduce.
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