That makes sense! Maybe we can make MapState implement Iterable interface, so that we can use foreach directly on MapState.
- Jark Wu > 在 2016年10月19日，下午5:48，SHI Xiaogang <shixiaoga...@gmail.com> 写道： > > Hi Jark > > If the state is very big, it may occupy a lot of memory if we return > Set<Map.Entry<K, V>>. > > By wrapping the returned iterator, we can easily implement a method > returning Iterable<Map.Entry<K, V>>. > Users can use that returned Iterable in the foreach loop. > > Regards > Xiaogang > > > > 2016-10-19 17:43 GMT+08:00 Jark Wu <wuchong...@alibaba-inc.com>: > >> Hi Xiaogang, >> >> I think maybe return Set<Map.Entry<K,V>> is better than >> Iterator<Map.Entry<K,V>>. >> Because users can use foreach on Set but not Iterator, and can use >> iterator access via set.iterator(). >> Maybe Map.entrySet() is a more familiar way to users. >> >> >> - Jark Wu >> >>> 在 2016年10月19日，下午5:18，SHI Xiaogang <shixiaoga...@gmail.com> 写道： >>> >>> Agreed. >>> >>> contains(K key) should be provided. >>> The iterator() method should return Iterator<Map.Entry<K, V>> instead of >>> Iterator<Tuple2<K, V>>. >>> >>> Besides, size() may also be provided. >>> >>> With these methods, MapStates appear very similar to Java Maps. Users >> will >>> be very happy to use them. >>> >>> Regards, >>> Xiaogang >>> >>> >>> 2016-10-19 16:55 GMT+08:00 Till Rohrmann <trohrm...@apache.org>: >>> >>>> Hi Xiaogang, >>>> >>>> I really like your proposal and think that this would be a valuable >>>> addition to Flink :-) >>>> >>>> For convenience we could maybe add contains(K key), too. >>>> >>>> Java's Map interface returns a Set of Entry when calling entrySet() >> (which >>>> is the equivalent of iterator() in our interface). The Entry interface >> not >>>> only allows to get access to the key and value of the map entry but also >>>> allows to set a value for the respective key via setValue (even though >> it's >>>> an optional operation). Maybe we want to offer something similar when >>>> getting access to the entry set via the iterator method. >>>> >>>> Cheers, >>>> Till >>>> >>>> On Wed, Oct 19, 2016 at 4:18 AM, SHI Xiaogang <shixiaoga...@gmail.com> >>>> wrote: >>>> >>>>> Hi, all. I created the JIRA https://issues.apache.org/ >>>>> jira/browse/FLINK-4856 to >>>>> propose adding MapStates into Flink. >>>>> >>>>> MapStates are very useful in our daily jobs. For example, when >>>> implementing >>>>> DistinctCount, we store the values into a MapState and the result of >> each >>>>> group(key) is exactly the number of entries in the MapState. >>>>> >>>>> In my opinion, the methods provided by the MapState may include: >>>>> * void put(K key, V value) >>>>> * V get(K key) >>>>> * Iterable<K> keys() >>>>> * Iterable<V> values() >>>>> * Iterator<Tuple2<K, V>> iterator() >>>>> >>>>> Do you have any comments? Any is appreciated. >>>>> >>>>> Xiaogang >>>>> >>>> >> >>
