I'm trying to filter a List with RxJava2 such that each item (object) in the list should pass a validation check and I get a resulting List with only items that pass that test. For instance if my Object had the following structure,
class MyClassA {
int value1;
int value2;
}
I want to only get the list of items where the value2
is 10.
I have an API call function that returns an Observable of List, i.e. Observable<List<MyClassA>>
as follows,
apiService.getListObservable()
.subscribeOn(Schedulers.io)
.observeOn(AndroidSchedulers.mainThread());
and I would like to have the output filtered, so I tried adding a .filter()
operator to the above but it seems to require a Predicate<List<MyClassA>>
instead of just a MyClassA
object with which I can check and allow only ones where value2 == 10
.
I'm pretty new to RxJava and RxJava2 and seems like I'm missing something basic here?
TIA
You can unroll the list and then collect up those entries that passed the filter:
apiService.getListObservable()
.subscribeOn(Schedulers.io)
.flatMapIterable(new Function<List<MyClassA>, List<MyClassA>>() {
@Override public List<MyClassA> apply(List<MyClassA> v) {
return v;
}
})
.filter(new Predicate<MyClassA>() {
@Override public boolean test(MyClassA v) {
return v.value2 == 10;
}
})
.toList()
.observeOn(AndroidSchedulers.mainThread())
.subscribe(...);
You may take a look at the below. It demonstrates the ways to print just the filtered objects OR the lists that contain filtered objects. Here the filtering logic is to retain the org.apache.commons.lang3.tuple.Pair
s that have even numbers in right.
public static void main(String[] args) {
// print raw output
getListObservable().subscribe(System.out::println);
// print the objects post filtering
getListObservable().flatMap(v -> Observable.from(v)).filter(p -> p.getRight()%2==0).subscribe(System.out::println);
// print the list refined with only filtered objects
getListObservable().flatMap(v -> Observable.just(v.stream().filter(p -> p.getRight()%2==0).collect(Collectors.toList()))).subscribe(System.out::println);
}
private static Observable<List<Pair<Integer, Integer>>> getListObservable() {
return Observable.create(subscriber -> {
for(int i=0; i<5; i++){
List<Pair<Integer, Integer>> list = new ArrayList<>();
for(int j=0; j<5; j++){
list.add(Pair.of(i, j));
}
subscriber.onNext(list);
}
});
}
Output with contents of observable:
[(0,0), (0,1), (0,2), (0,3), (0,4)]
[(1,0), (1,1), (1,2), (1,3), (1,4)]
[(2,0), (2,1), (2,2), (2,3), (2,4)]
[(3,0), (3,1), (3,2), (3,3), (3,4)]
[(4,0), (4,1), (4,2), (4,3), (4,4)]
Output to contain only filtered objects:
(0,0)
(0,2)
(0,4)
(1,0)
(1,2)
(1,4)
(2,0)
(2,2)
(2,4)
(3,0)
(3,2)
(3,4)
(4,0)
(4,2)
(4,4)
Output to contain the lists that contain only filtered objects.
[(0,0), (0,2), (0,4)]
[(1,0), (1,2), (1,4)]
[(2,0), (2,2), (2,4)]
[(3,0), (3,2), (3,4)]
[(4,0), (4,2), (4,4)]