wangpeibin713 edited a comment on issue #7786: [FLINK-11706] Add the 
SumFunction to support KeyedStream.sum
URL: https://github.com/apache/flink/pull/7786#issuecomment-465968792
 
 
   ```
   DataStream<Tuple2<Long, Integer[]>> src = env.fromCollection(Arrays.asList(
        new Tuple2<>(1L, new Integer[]{2, 4}),
        new Tuple2<>(1L, new Integer[]{3, 6}),
        new Tuple2<>(1L, new Integer[]{4, 8})
   ));
   ```
   with the flatmap function as your code, the output of the datastream (show 
above) is :
   ```
   (1,2)
   (1,6)
   (1,9)
   (1,15)
   (1,19)
   (1,27)
   ```
   
   my expected output is :
   ```
   (1,[2, 4])
   (1,[5, 10])
   (1,[9, 18])
   ```
                
   > How about the below code
   > 
   > ```
   > src.flatMap(new FlatMapFunction<Tuple2<Long, Integer[]>, Tuple2<Long, 
Integer>>() {
   >    @Override
   >    public void flatMap(Tuple2<Long, Integer[]> value, 
Collector<Tuple2<Long, Integer>> out) throws Exception {
   >        for (Integer v : value.f1) {
   >            out.collect(new Tuple2<>(value.f0, v));
   >             }
   >    }
   >     }).keyBy(0)
   >     .sum(1)
   >     .print();
   > ```
   
   

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