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From danielblazevski <...@git.apache.org>
Subject [GitHub] flink pull request #2368: [FLINK-3899] Document window processing with Reduc...
Date Wed, 24 Aug 2016 17:34:23 GMT
Github user danielblazevski commented on a diff in the pull request:

    --- Diff: docs/apis/streaming/windows.md ---
    @@ -459,42 +459,106 @@ ready for processing. This allows to get the benefit of incremental
window compu
     the additional meta information that writing a `WindowFunction` provides.
     This is an example that shows how incremental aggregation functions can be combined with
    -a `WindowFunction`.
    +a `WindowFunction`.  The `FoldFunction`/`WindowFunction` example shows how to extract
    +ending event-time of a window of sensor readings that contain a timestamp, 
    +and the `ReduceFunction`/`WindowFunctions` example shows how to do eager window
    +aggregation (only a single element is kept in the window).
     <div class="codetabs" markdown="1">
     <div data-lang="java" markdown="1">
     {% highlight java %}
    -DataStream<Tuple2<String, Long>> input = ...;
    +DataStream<SensorReading> input = ...;
     // for folding incremental computation
         .keyBy(<key selector>)
         .window(<window assigner>)
    -    .apply(<initial value>, new MyFoldFunction(), new MyWindowFunction());
    +    .apply(Long.MIN_VALUE, new MyFoldFunction(), new MyWindowFunction());
    +/* ... */
    +private static  class myFoldFunction implements FoldFunction<SensorReading, Long>
    +    public Long fold(Long acc, SensorReading s) {
    +        return Math.max(acc, s.timestamp());
    +    }
    +private static class MyWindowFunction implements WindowFunction<Long, Long, String,
TimeWindow> {
    +    public void apply(String key, TimeWindow window, Iterable<Long> timestamps,
Collector<Long> out) {
    +            out.collect(timestamps.iterator().next());
    --- End diff --
    Made the changes in the Java version and added the comments.  Had some issues with the
Scala version.  See screenshots, the only change is really to change to the type of `Iterable`
in the `WindowFunction`, which IntelliJ was saying has to have type `SensorReadng`, which
is not ideal.  I removed the Scala version for now.  
    <img width="426" alt="screenshot 2016-08-24 13 28 12" src="https://cloud.githubusercontent.com/assets/10012612/17940967/4a025738-69ff-11e6-9354-31c2ead563d4.png">
    <img width="625" alt="screenshot 2016-08-24 13 27 51" src="https://cloud.githubusercontent.com/assets/10012612/17940972/4dd5db28-69ff-11e6-8c6a-11b1900796ad.png">

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