code: public Iterable<Map.Entry<Integer, Record>> entries() {
          return () -> new Iterator<Map.Entry<Integer, Record>>() {
              private final Iterator<Map.Entry<Integer, Record>> it = data.records.entrySet().iterator();
  
              /** {@inheritDoc} */
              @Override
              public boolean hasNext() {
                  return it.hasNext();
              }
  
              /** {@inheritDoc} */
              @Override
              public Map.Entry<Integer, Record> next() {
                  return it.next();
              }
  
              /** {@inheritDoc} */
              @Override
              public void remove() {
                  throw new UnsupportedOperationException("This is a read-only iterator, remove operation is not supported.");
              }
          };
      }
docs: Returns a read-only Iterable on the keys and Records of the Dataframe.
  
  @return