code: public void fit(@NonNull MultiDataSetIterator iterator) {
          List<S.Builder> featureNormBuilders = new ArrayList<>();
          List<S.Builder> labelNormBuilders = new ArrayList<>();
  
          iterator.reset();
          while (iterator.hasNext()) {
              MultiDataSet next = iterator.next();
              fitPartial(next, featureNormBuilders, labelNormBuilders);
          }
  
          featureStats = buildList(featureNormBuilders);
          if (isFitLabel()) {
              labelStats = buildList(labelNormBuilders);
          }
      }
docs: Fit an iterator
  
  @param iterator for the data to iterate over