js8544 commented on code in PR #36020:
URL: https://github.com/apache/arrow/pull/36020#discussion_r1225201776
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cpp/src/arrow/compute/api_vector.h:
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@@ -210,21 +210,29 @@ class ARROW_EXPORT PartitionNthOptions : public
FunctionOptions {
NullPlacement null_placement;
};
-/// \brief Options for cumulative sum function
-class ARROW_EXPORT CumulativeSumOptions : public FunctionOptions {
+/// \brief Options for cumulative functions
+/// \note Also aliased as CumulativeSumOptions for backward compatibility
+class ARROW_EXPORT CumulativeOptions : public FunctionOptions {
public:
- explicit CumulativeSumOptions(double start = 0, bool skip_nulls = false);
- explicit CumulativeSumOptions(std::shared_ptr<Scalar> start, bool skip_nulls
= false);
- static constexpr char const kTypeName[] = "CumulativeSumOptions";
- static CumulativeSumOptions Defaults() { return CumulativeSumOptions(); }
-
- /// Optional starting value for cumulative operation computation
- std::shared_ptr<Scalar> start;
+ explicit CumulativeOptions(bool skip_nulls = false);
+ explicit CumulativeOptions(double start, bool skip_nulls = false);
+ explicit CumulativeOptions(std::shared_ptr<Scalar> start, bool skip_nulls =
false);
+ static constexpr char const kTypeName[] = "CumulativeOptions";
+ static CumulativeOptions Defaults() { return CumulativeOptions(); }
+
+ /// Optional starting value for cumulative operation computation, default
depends on the
+ /// operation and input type.
+ /// - sum: 0
+ /// - prod: 1
+ /// - min: maximum of the input type
+ /// - max: minimum of the input type
+ std::optional<std::shared_ptr<Scalar>> start;
Review Comment:
The current implementation defaults `start` to a DoubleScalar with value
zero. This is undesirable because:
1. An unnecessary `Cast` needs to happen if input type is not double.
2. For min and max we can't determine the default start value before input
type is known.
So I changed this to an optional. If it is not set, the kernel will
determine the start value at initialization. It's implemented with templates so
there is zero cost.
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