fn column_groups(
column: SEXP,
col: &str,
) -> Result<Vec<(GroupKey, Vec<usize>)>, DataFrameError>Expand description
One supported key column’s groups, in single-column group order (NA last)
— the per-type dispatch behind DataFrame::group_by, and through
column_keys / row_keys behind group_by_multi and
group_by_metadata.