An example how to iterate and filter through list which is inside object, retrieved from server/etc with RxJava

FilterListInsideResponse.java

public Observable<SomeResponse> downloadAndFilterListInResponse() {
    return mSomeRetrofitApi.downloadSomeData() // get response from server/etc
            // start iterating through list in response object
            .flatMap(response -> Observable.from(response.getListWeWantToFilterOut()) 
                    // NOTE: this is inner sequence, gets result from Observable.from
                    .filter(item -> item != null) // filters out items that are null
                    .toList() // all items combined into list again
                    .take(100) // take only first 100 items, rest will be ignored
                    .map(items -> { // now we need to 'map' list into response
                        response.setListWeWantToFilterOut(items); // overwrite list in object with filtered list
                        return response; // return modified response
                    }));
}

    public class SomeResponse {

        private List<String> listWeWantToFilterOut;
        private int someIntegerWeWantToKeep;
        private String someOtherValueWeWantToKeep;

        public List<String> getListWeWantToFilterOut() {
            return listWeWantToFilterOut;
        }

        // in this example list must has required access
        public void setListWeWantToFilterOut(List<String> listWeWantToFilterOut) {
            this.listWeWantToFilterOut = listWeWantToFilterOut;
        }

    }