Github user arunmahadevan commented on a diff in the pull request:
https://github.com/apache/storm/pull/2233#discussion_r130434218
--- Diff: storm-client/src/jvm/org/apache/storm/streams/PairStream.java ---
@@ -380,6 +383,25 @@
return partitionBy(KEY).updateStateByKeyPartition(stateUpdater);
}
+ /**
+ * group the values of this stream with the values having the same key
from the other stream.
+ * <p>
+ * Note: The parallelism of this stream is carried forward to the
joined stream.
+ * </p>
+ *
+ * @param otherStream the other stream
+ * @param valueJoiner the {@link PairValueJoiner}
+ * @param <R> the type of the values resulting from the
grouping
+ * @param <V1> the type of the values in the other stream
+ * @return the new stream
+ */
+ public <R, V1> PairStream<K, R> coGroupByKey(PairStream<K, V1>
otherStream,
+
PairValueJoiner<Collection<V>, Collection<V1>> valueJoiner) {
--- End diff --
In the case of Co-group it does not make much sense to expose the
PairValueJoiner in the public API. If needed this can be an implementation
detail.
So the API could be something like,
```java
public <V1> PairStream<K, Pair<Iterable<V>, Iterable<V1>>>
coGroupByKey(PairStream<K, V1> otherStream)
```
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