[C++][Statistics] How to distinct "utf8" and "binary" in arrow::ArrayStatistics?

[kou]

Describe the enhancement requested

We can represent "utf8" and "binary" min/max values by arrow::ArrayStatistics:

arrow/cpp/src/arrow/array/statistics.h

Lines 29 to 67 in 4c36f12

	/// \brief Statistics for an Array
	///
	/// Apache Arrow format doesn't have statistics but data source such
	/// as Apache Parquet may have statistics. Statistics associated with
	/// data source can be read unified API via this class.
	struct ARROW_EXPORT ArrayStatistics {
	using ValueType = std::variant<bool, int64_t, uint64_t, double, std::string>;
	/// \brief The number of null values, may not be set
	std::optional<int64_t> null_count = std::nullopt;
	/// \brief The number of distinct values, may not be set
	std::optional<int64_t> distinct_count = std::nullopt;
	/// \brief The minimum value, may not be set
	std::optional<ValueType> min = std::nullopt;
	/// \brief Whether the minimum value is exact or not
	bool is_min_exact = false;
	/// \brief The maximum value, may not be set
	std::optional<ValueType> max = std::nullopt;
	/// \brief Whether the maximum value is exact or not
	bool is_max_exact = false;
	/// \brief Check two statistics for equality
	bool Equals(const ArrayStatistics& other) const {
	return null_count == other.null_count && distinct_count == other.distinct_count &&
	min == other.min && is_min_exact == other.is_min_exact && max == other.max &&
	is_max_exact == other.is_max_exact;
	}
	/// \brief Check two statistics for equality
	bool operator==(const ArrayStatistics& other) const { return Equals(other); }
	/// \brief Check two statistics for not equality
	bool operator!=(const ArrayStatistics& other) const { return !Equals(other); }
	};

But we can't distinct them because we use std::string in ValueType for both of them.

How can we distinct them? Should we add arrow::ArrayStatistics::{min,max}_type?

Component(s)

C++

[pitrou]

Why would we want to distinguish them?

[kou]

I wanted this when I create an arrow::DataType for arrow::ArrayStatistics.
But I may use associated arrow::Array information for it. I'll try it.

[kou]

Issue resolved by pull request 45094
#45094