fn column_level_order(column: SEXP) -> Vec<GroupKey>Expand description
Distinct non-NA keys of one column in single-column group order (factor level
order incl. empty levels; byte-sorted characters; numeric integers; FALSE
then TRUE). NA is excluded — interaction() drops NA rows and NA-containing
tuples are ordered separately. Reuses the single-column bucketers so the
per-column order stays byte-identical to DataFrame::group_by. Only reached
for supported columns (column_keys rejects the rest first).