I also support this approach: ds.groupBy(0).aggregate(min(1), max(1), cnt())
I think it makes the code more readable, because it is easy to see whats in the result tuple. Gyula > On 10 Nov 2014, at 10:49, Aljoscha Krettek <aljos...@apache.org> wrote: > > I like this version: ds.groupBy(0).aggregate(min(1), max(1), cnt()), > very concise. > > On Mon, Nov 10, 2014 at 10:42 AM, Viktor Rosenfeld > <viktor.rosenf...@tu-berlin.de> wrote: >> Hi Fabian, >> >> I ran into a problem with your syntax example: >> >> DataSet<Tuple2<String, Integer>> ds = ... >> DataSet<Tuple4<Tuple2<String,Integer>,Integer, Integer, Long> result = >> ds.groupBy(0).min(1).andMax(1).andCnt(); >> >> Basically, in the example above we don't know how long the chain of >> aggregation method calls is. Also, each aggregation method call adds a >> field to the result tuple (the first call to groupBy returns a >> Tuple1). Because the resultType of an operator is specified in the >> constructur, every one of those method calls needs to create a new >> Operator<OUT> with the correct result type. However, only the >> translateToDataflow method of the last method call in the chain should >> actually compute the aggregation. >> >> This can be achieved by testing if an aggregation method is called on >> an AggregationOperator. The translateToDataFlow method of the >> operators in the start/middle of the chain would then just return a >> MapOperatorBase which simply extends the tuple. The >> translateToDataFlow method of the last operator in the chain would >> return a GroupReduceOperatorBase. >> >> This strategy seems very hackish and involves lots of unnecessary >> copying of tuple data. I think a better way would be to use the >> following syntax: >> >> ds.groupBy(0).aggregate(min(1), max(1), cnt()) >> >> or >> >> ds.groupBy(0).min(1).max(1).cnt(1).aggregate() >> >> Here, there is only one method which creates a new operator, the >> aggregate method, and the final resultType is known when aggregate is >> called. >> >> What do you think? >> >> Best, >> Viktor >> >> >> >> -- >> View this message in context: >> http://apache-flink-incubator-mailing-list-archive.1008284.n3.nabble.com/Hi-Aggregation-support-tp2311p2429.html >> Sent from the Apache Flink (Incubator) Mailing List archive. mailing list >> archive at Nabble.com.
