docs: public static <A, B> CountAccumulator<B> getFeatureCounts(FeatureGenerator<A, B> featureGenerator,
        Collection<? extends A> data) {
      MapReduceExecutor executor = MapReduceConfiguration.getMapReduceExecutor();
      Mapper<A, Map<B, Double>> mapper = new FeatureCountMapper<A, B>(featureGenerator);
      Reducer<Map<B, Double>, CountAccumulator<B>> reducer = new FeatureCountReducer<B>();
      return executor.mapReduce(data, mapper, reducer);
    }