Function UniqueValueCount

tests/cpp/common/test_quantile.h:458–458

inline double TotalWeight(ReferenceColumn const& col) { return col.prefix_weights.back(); }

inline std::size_t UniqueValueCount(ReferenceColumn const& col) { return col.values.size(); }

inline bool EmptyReference(ReferenceColumn const& col) { return col.values.empty(); }