I have to admit that the difference between the two methods is subtle, and in my opinion it doesn't make much sense to have the two variants.
- max() returns a tuple with the max value at the specified position, the other fields of the tuple/pojo are undefined - maxBy() returns a tuple with the max value at the specified position (the other fields are retained) On Mon, Aug 8, 2016 at 2:55 PM, Claudia Wegmann <c.wegm...@kasasi.de> wrote: > OK, found my mistake reagarding question 2.). I key by the id value and > gave all the data sets different values there. So of course all 4 data sets > are printed. Sorry J > > But question 1.) still remains. > > > > *Von:* Claudia Wegmann [mailto:c.wegm...@kasasi.de] > *Gesendet:* Montag, 8. August 2016 14:27 > *An:* user@flink.apache.org > *Betreff:* max aggregator dosen't work as expected > > > > Hey, > > > > I have some questions to aggregate functions such as max or min. Take the > following example: > > > > //create Stream with event time where Data contains an ID, a timestamp and > a temperature value > > DataStream<Data> oneStream = env.fromElements( > > *new *Data(123, *new *Date(116, 8,8,11,11,11), 5), > > *new *Data(124, *new *Date(116, 8,8,12,10,11), 8), > > *new *Data(125, *new *Date(116, 8,8,12,12,11), 10), > > *new *Data(126, *new *Date(116, 8,8,12,15,11), 2)) > > .assignTimestampsAndWatermarks(*new *AscendingTimestampExtractor<Data>() { > @Override > *public long *extractAscendingTimestamp(*final *Data data) { > *return *data.getTimestamp().getTime(); > } > }); > > > > //calluclate max value of temperature per hour > > DataStream<Data> maxStream = WatermarkStream > > .keyBy(*"id"*) > > .timeWindow(Time.*hours*(1)) > > .max(*"temp"*); > maxStream.print(); > > > > > > Here are the questions I ran into: > > 1.) Why does the resulting stream “maxStream” have to be of type Data? > From the documentation and the difference to maxBy I would expect the > resulting stream to be of type Integer? > > 2.) Executing the code as it is above, I would expect the printed > result be the data with ID 124 and ID 125. However, the execution prints > all 4 data sets. Did I totally get this example wrong? How would the code > need to look, to get the expected result? > > 3.) Can you point me to a good example for using time windows and > aggregates? I couldn’t find one that explains the above questions. > > > > Thanks for your help and best wishes, > > Claudia > > > > > > >
