This should directly go into the API, IMO.
As I said, there are several open JIRAs for this issue.
2015-01-21 22:29 GMT+01:00 Felix Neutatz <neut...@googlemail.com>:
> Thanks, @Fabian, your workaround works :)
>
> But I think this feature is really missing. Shall we add this functionality
> natively or via the proposed lib package?
>
> 2015-01-21 20:38 GMT+01:00 Fabian Hueske <fhue...@gmail.com>:
>
> > Chesnay is right.
> > Right now, it is not possible to do want you want in a straightforward
> way
> > because Flink does not support to fully sort a data set (there are
> several
> > related issues in JIRA).
> >
> > A workaround would be to attach a constant value to each tuple, group on
> > that (all tuples are sent to the same group), sort that group, and apply
> > the first operator.
> >
> > 2015-01-21 20:22 GMT+01:00 Chesnay Schepler <
> chesnay.schep...@fu-berlin.de
> > >:
> >
> > > If i remember correctly first() returns the first n values for every
> > > group. the javadocs actually don't make this behaviour very clear.
> > >
> > >
> > > On 21.01.2015 19:18, Felix Neutatz wrote:
> > >
> > >> Hi,
> > >>
> > >> my use case is the following:
> > >>
> > >> I have a Tuple2<String,Long>. I want to group by the String and sum up
> > the
> > >> Long values accordingly. This works fine with these lines:
> > >>
> > >> DataSet<Lineitem> lineitems = getLineitemDataSet(env);
> > >> lineitems.project(new int
> > []{3,0}).groupBy(0).aggregate(Aggregations.SUM,
> > >> 1);
> > >>
> > >> After the aggregation I want to print the 10 groups with the highest
> > sum,
> > >> like:
> > >>
> > >> string1, 100L
> > >> string2, 50L
> > >> string3, 1L
> > >>
> > >> I tried that:
> > >>
> > >> lineitems.project(new int
> > []{3,0}).groupBy(0).aggregate(Aggregations.SUM,
> > >> 1).groupBy(0).sortGroup(1, Order.DESCENDING).first(3).print();
> > >>
> > >> But instead of 3 records, I get a lot more.
> > >>
> > >> Can see my error?
> > >>
> > >> Best regards,
> > >>
> > >> Felix
> > >>
> > >>
> > >
> >
>
