class GraphsInteractor {

    public Maybe<GraphUiIndicator> getSummationByCategories(Trip trip) {
        return groupingController.getSummationByCategoryAsGraphEntries(trip)
                .filter(graphEntries -> !graphEntries.isEmpty())
                .flatMapSingleElement(Single::just)
                .map(GraphUiIndicator::summationByCategory)
                .observeOn(AndroidSchedulers.mainThread());
    }

    @Inject public  GraphsInteractor(Context context, GroupingController groupingController);

}