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From Yassine MARZOUGUI <y.marzou...@mindlytix.com>
Subject Questions about FoldFunction and WindowFunction
Date Wed, 02 Nov 2016 09:42:16 GMT
Hi all,

I have a couple questions about FoldFunction and WindowFunction:

1. When using a RichFoldFunction after a window as in
keyedStream.window().fold(new
RichFoldFunction()), is the close() method called after each window or
after all the windows for that key are fired?

2. When applying a FoldFunction to a window followed by a WindowFunction
via apply
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/datastream/WindowedStream.html#apply-R-org.apache.flink.api.common.functions.FoldFunction-org.apache.flink.streaming.api.functions.windowing.WindowFunction->(R
initialValue,
FoldFunction
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/api/common/functions/FoldFunction.html>
<T
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/datastream/WindowedStream.html>,R>
foldFunction,
WindowFunction
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/functions/windowing/WindowFunction.html>
<R,R,K
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/datastream/WindowedStream.html>
,W
<https://ci.apache.org/projects/flink/flink-docs-master/api/java/org/apache/flink/streaming/api/datastream/WindowedStream.html>
> function), why should the output of the WindowFunction be of the same
type as the input? It would be practical to have a different output type
sometimes, for example one would fold tuples in the FoldFunction and then
process the (only) aggregated tuple in the Window function and emit an
Integer.

Best,
Yassine

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