# Buggy code
def groupby_reduce(
    self, axis, by, map_func, reduce_func, new_index=None, new_columns=None
):
    """Groupby another dataframe and aggregate the result.

    Args:
        axis: The axis to groupby and aggregate over.
        by: The dataframe to group by.
        map_func: The map component of the aggregation.
        reduce_func: The reduce component of the aggregation.
        new_index: (optional) The index of the result. We may know this in advance,
            and if not provided it must be computed.
        new_columns: (optional) The columns of the result. We may know this in
            advance, and if not provided it must be computed.

    Returns:
         A new dataframe.
    """
    new_partitions = self._frame_mgr_cls.groupby_reduce(
        axis, self._partitions, by._partitions, map_func, reduce_func
    )
    if new_columns is None:
        new_columns = self._frame_mgr_cls.get_indices(
            1, new_partitions, lambda df: df.columns
        )
    if new_index is None:
        new_index = self._frame_mgr_cls.get_indices(
            0, new_partitions, lambda df: df.index
        )
    return self.__constructor__(new_partitions, new_index, new_columns)


# Traceback (Exception)
Traceback (most recent call last):
File "test.py", line 15, in <module>
print(f"modin:\n{modin_df.sum(min_count=1)}")
File "modin\pandas\base.py", line 3512, in __str__
return repr(self)
File "modin\pandas\series.py", line 307, in __repr__
temp_df = self._build_repr_df(num_rows, num_cols)
File "modin\pandas\base.py", line 108, in _build_repr_df
return self.iloc[indexer]._query_compiler.to_pandas()
File "modin\backends\pandas\query_compiler.py", line 191, in to_pandas
return self._modin_frame.to_pandas()
File "modin\engines\base\frame\data.py", line 1801, in to_pandas
"Internal and external indices do not match.",
File "modin\error_message.py", line 54, in catch_bugs_and_request_email
" caused this error.\n{}".format(extra_log)
Exception: Internal Error. Please email bug_reports@modin.org with the traceback and command that caused this error.
Internal and external indices do not match.

# Fixed code
def groupby_reduce(
    self, axis, by, map_func, reduce_func, new_index=None, new_columns=None
):
    """Groupby another dataframe and aggregate the result.

    Args:
        axis: The axis to groupby and aggregate over.
        by: The dataframe to group by.
        map_func: The map component of the aggregation.
        reduce_func: The reduce component of the aggregation.
        new_index: (optional) The index of the result. We may know this in advance,
            and if not provided it must be computed.
        new_columns: (optional) The columns of the result. We may know this in
            advance, and if not provided it must be computed.

    Returns:
         A new dataframe.
    """
    new_partitions = self._frame_mgr_cls.groupby_reduce(
        axis, self._partitions, by._partitions, map_func, reduce_func
    )
    new_axes = [
        self._compute_axis_labels(i, new_partitions) if new_axis is None else new_axis
        for i, new_axis in enumerate([new_index, new_columns])
    ]

    return self.__constructor__(new_partitions, *new_axes)