booksWithSubjectsSelector.js

const booksWithSubjectsSelector = createSelector(
    [state => state.books.list, state => state.subjects.list],
    setBookResultsSubjects
);

const stackedSubjectsSelector = createSelector(
    [state => state.list],
    stackAndGetTopLevelSubjects
);

const bookListSelector = state => ({
    subjects: Object.assign({}, state.bookList.subjects, {list: stackedSubjectsSelector(state.bookList.subjects)}),
    books: Object.assign({}, state.bookList.books, {list: booksWithSubjectsSelector(state.bookList)}),
    filters: state.bookList.filters
});