java 8 streams grouping and creating Map> issue

Question

This is the method I followed,

data.stream().collect(Collectors
                .groupingBy(SubscriberActivityAggData::getSubscriberAddress
                        , Collectors.mapping(SubscriberActivityAggData::getAppId, Collectors.toSet())));

but the Set contains only one unique value.

but when I use Collectors.toList all values are obtained.

data.stream().collect(Collectors
            .groupingBy(SubscriberActivityAggData::getSubscriberAddress
                    , Collectors.mapping(SubscriberActivityAggData::getAppId, Collectors.toList())));

is there an issue with the implementation, I want to get the unique set of appIds.

I want to obtain all the unique app Ids, there are duplicate records with the same app ids in the data object. It's a List<SubscriberActivityAggData> of objects.

this is the object structure

   @Column(name = "subscriber_address")
    String subscriberAddress;

    @Column(name = "event_time")
    Date eventTime;

    @Column(name = "app_id")
    String appId;

Input "data" variable

SubscriberActivityAggData{subscriberAddress='77123456', eventTime=Thu Nov 14 00:39:04 IST 2019, appId='APP_999674357'}
SubscriberActivityAggData{subscriberAddress='77123456', eventTime=Sun Nov 10 07:45:51 IST 2019, appId='APP_999001564'}
SubscriberActivityAggData{subscriberAddress='77876', eventTime=Wed Nov 13 00:32:51 IST 2019, appId='APP_999542061'}
SubscriberActivityAggData{subscriberAddress='77876', eventTime=Sun Nov 10 13:55:22 IST 2019, appId='APP_999772967'}

Current Output

77876 -> APP_999772967
77123456 -> APP_999001564

Expected Output

77876 -> APP_999772967,APP_999542061
77123456 -> APP_999001564,APP_999674357

You are not using `Collectors.toList` in the code you posted. — Eran, Jul 15 '20 at 12:08
Why don't you use `groupingBy` as in the example stream you where following? — Herr Derb, Jul 15 '20 at 12:10
*Set contains only one unique value.*, what's wrong in it? It is supposed to include unique values only, right? — Naman, Jul 15 '20 at 12:15
I'm confused. Could you explain once again what you want to achieve here? In the last sentence you said that you want to get a set. Why do you use/want to use `Collectors.toList` then? — Amongalen, Jul 15 '20 at 12:16
@Naman there are records with the same field duplicated appId, I want to get the unique appIds that's why I want to use a set — Windula Kularatne, Jul 15 '20 at 12:26
If you want to get a set then what's wrong with the first snippet you posted? — Amongalen, Jul 15 '20 at 12:27
and the first block of code doesn't work? why? can you add sample input and expected output to your question as well. — Naman, Jul 15 '20 at 12:28
@Naman I added a sample input and output. seems like it's overwriting — Windula Kularatne, Jul 15 '20 at 12:42
The edit further confuses me on how are you expecting the output you've mentioned. — Naman, Jul 15 '20 at 12:45

java 8 streams grouping and creating Map> issue

0 Answers0