Convert rxJava List to Map

Question

I have a list coming back from a REST endpoint. I need to break this list down into categories (a category is an element in every entry in the list). Certain categories will be cached for faster retrieval later.

I did not know if I could make .map () entries and provide some filters () or some type of case-case to place category entries in the right bucket.

Is it wise to implement something like this sound using rxJava?

UPDATE: Non-working version

private Map<String, List<VideoMetadataInfoEntity>> buildCategories( Observable<List<VideoMetadataInfoEntity>> videoList ) {

    Map<String, List<VideoMetadataInfoEntity>> categoryMap = new HashMap<>();
    videoList
            .flatMap( Observable::from )
            .subscribe( videoMetadataInfoEntity -> mapCategory(videoMetadataInfoEntity, categoryMap ) );

    Observable.just( categoryMap )
            .doOnNext( saveCategoriesToCacheAction );

    return categoryMap;
}

However, this fire is in order, and this is my understanding, the second observable does not send anything saveCategoriesToCacheAction, since it is not subscribed to the result of the first observable.

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Answer 1

:

Observable.range(1, 20)
            .groupBy(number -> number % 2)
            .flatMap(groupedObservable -> groupedObservable.toList())
            .toMap(list -> list.get(0) % 2);

[{0=[2, 4, 6, 8, 10, 12, 14, 16, 18, 20], 1=[1, 3, 5, 7, 9, 11, 13, 15, 17, 19]}]

:

• (1, 20) - ,
• groupBy ( → % 2) - , , , ( x% 2)
• flatMap (groupedObservable → groupedObservable.toList()) - ,
• toMap (list → list.get(0)% 2) -

Answer 2

groupBy ( ).

Map<Integer, List<Integer>> groupedValues = new HashMap<>(4);
    Observable.range(1, 20)
            .groupBy(i -> i % 2, i -> i)
            .subscribe(go -> {
                List<Integer> groupValues = new ArrayList<>();
                groupedValues.put(go.getKey(), groupValues);
                go.subscribe(t -> add(t, groupValues));
            });

:

-, 1 20 ( range) (groupBy, GroupedObservable) , ( onNext) , , .

take(0) , .

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Answer 3

RxJava , , api. Java 8, , , , , Java 7.

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Observable.from(list).subscribe(item -> groupItemInCategoryBucket(item));

groupItemInCategoryBucket - , switch .

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