What does the number in front of ">" mean when I print a DataStream

[chrisr123]

What does the number in front of the ">" character  mean when call print()
on a dataset?

For example I may have this in my source where I am reading a socket stream
of sensor data:

                DataStream<Tuple2&lt;String,Double>> simpleStream = env
                                .socketTextStream(parms.get("host"), 
parms.getInt("port"))
                                .map(new SensorParser());

                DataStream<Tuple2&lt;String,Double>> temps = simpleStream
                                .keyBy(0)
                                
.window(TumblingProcessingTimeWindows.of(Time.seconds(10)))
                                .process(new 
MyProcessWindowFunction(appStartTime));
                temps.print();

When I look at the output, I see something like:

1> (sensor5,98.64)
3> (sensor8,81.31)
2> (sensor3,69.55)
4> (sensor0,82.86)

What do numbers 1,3,2,4 mean, i.e. 1>, 3>, 2>, 4> on the lines above?
Thanks





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