docs: public Map<U, Double> getActiveFeatures(Tensor featureVector) {
      Preconditions.checkArgument(featureVector.getDimensionSizes().length == 1
          && featureVector.getDimensionSizes()[0] == getNumberOfFeatures());
  
      Map<U, Double> features = Maps.newHashMap();
      Iterator<KeyValue> keyValueIter = featureVector.keyValueIterator();
      while (keyValueIter.hasNext()) {
        KeyValue featureKeyValue = keyValueIter.next();
        features.put(featureIndexes.get(featureKeyValue.getKey()[0]), featureKeyValue.getValue());
      }
      return features;
    }