code: public Integer set(Integer rId, Record r) {
          _unsafe_set(rId, r);
          updateMeta(r);
          return rId;
      }
docs: Sets the record of a particular id in the dataset. If the record does not
  exist it will be added with the specific id and the next added record will
  have as id the next integer.
  
  Note that the meta-data are partially updated. This means that if the replaced
  Record contained a column which is now no longer available in the dataset,
  then the meta-data will not refect this update (the column will continue to exist
  in the meta data). If this is a problem, you should call the recalculateMeta()
  method to force them being recalculated.
  
  @param rId
  @param r
  @return