Hi Maximilian, I tried your solution but it doesn't work because the rightElements iterator cannot be used more than once:
Caused by: org.apache.flink.util.TraversableOnceException: The Iterable can be iterated over only once. Only the first call to 'iterator()' will succeed. On Wed, Apr 15, 2015 at 12:59 PM, Maximilian Michels <m...@apache.org> wrote: > Hi Flavio, > > Here's an simple example of a Left Outer Join: > https://gist.github.com/mxm/c2e9c459a9d82c18d789 > > As Stephan pointed out, this can be very easily modified to construct a > Right Outer Join (just exchange leftElements and rightElements in the two > loops). > > Here's an excerpt with the most important part, the coGroup function: > > public static class LeftOuterJoin implements CoGroupFunction<Tuple2<Integer, > String>, Tuple2<Integer, String>, Tuple2<Integer, Integer>> { > > @Override > public void coGroup(Iterable<Tuple2<Integer, String>> leftElements, > Iterable<Tuple2<Integer, String>> rightElements, > Collector<Tuple2<Integer, Integer>> out) throws > Exception { > > final int NULL_ELEMENT = -1; > > for (Tuple2<Integer, String> leftElem : leftElements) { > boolean hadElements = false; > for (Tuple2<Integer, String> rightElem : rightElements) { > out.collect(new Tuple2<Integer, Integer>(leftElem.f0, > rightElem.f0)); > hadElements = true; > } > if (!hadElements) { > out.collect(new Tuple2<Integer, Integer>(leftElem.f0, > NULL_ELEMENT)); > } > } > > } > } > > > > On Wed, Apr 15, 2015 at 11:01 AM, Stephan Ewen <se...@apache.org> wrote: > >> I think this may be a great example to add as a utility function. >> >> Or actually add as an function to the DataSet, internally realized as a >> special case of coGroup. >> >> We do not have a ready example of that, but it should be straightforward >> to realize. Similar as for the join, coGroup on the join keys. Inside the >> coGroup function, emit the combination of all values from the two >> iterators. If one of them is empty (the one that is not outer) then emit >> all values from the outer side. >> >> Greetings, >> Stephan >> >> >> On Wed, Apr 15, 2015 at 10:36 AM, Flavio Pompermaier < >> pomperma...@okkam.it> wrote: >> >>> Do you have an already working example of it? :) >>> >>> >>> On Wed, Apr 15, 2015 at 10:32 AM, Ufuk Celebi <u...@apache.org> wrote: >>> >>>> >>>> On 15 Apr 2015, at 10:30, Flavio Pompermaier <pomperma...@okkam.it> >>>> wrote: >>>> >>>> > >>>> > Hi to all, >>>> > I have to join two datasets but I'd like to keep all data in the left >>>> also if there' no right dataset. >>>> > How can you achieve that in Flink? maybe I should use coGroup? >>>> >>>> Yes, currently you have to implement this manually with a coGroup >>> >>> >>> >> >
