message: Added static_assert to a couple of places
diff: @@ -405,6 +405,9 @@ template<typename ... types>
  void
  DataFrame<TS, HETERO>::remove_data_by_idx (Index2D<TS> range) {
  + static_assert(std::is_base_of<HeteroVector, HETERO>::value,
  + "Only a StdDataFrame can call remove_data_by_idx()");
  +
  const auto &lower =
  std::lower_bound (timestamps_.begin(), timestamps_.end(), range.begin);
  const auto &upper =
  @@ -435,6 +438,9 @@ template<typename ... types>
  void
  DataFrame<TS, HETERO>::remove_data_by_loc (Index2D<int> range) {
  + static_assert(std::is_base_of<HeteroVector, HETERO>::value,
  + "Only a StdDataFrame can call remove_data_by_loc()");
  +
  if (range.begin < 0)
  range.begin = static_cast<int>(timestamps_.size()) + range.begin;
  if (range.end < 0)
  