Copilot commented on code in PR #45001:
URL: https://github.com/apache/arrow/pull/45001#discussion_r3969083947
##########
docs/source/cpp/compute.rst:
##########
@@ -1282,6 +1282,27 @@ Containment tests
* \(8) Output is true iff :member:`MatchSubstringOptions::pattern`
matches the corresponding input element at any position.
+Hash Functions
+~~~~~~~~~~~~~~
+
+Not to be confused with the "group by" functions, hash functions produce an
array of hash
+values corresponding to the length of the input. Currently, these functions
take a single
+array as input.
Review Comment:
This section says the hash functions take a single array as input, but
`hash32`/`hash64` also accept Scalar and ChunkedArray inputs (returning the
same shape). The docs should describe the more general Datum contract to avoid
misleading users.
##########
cpp/src/arrow/compute/api_scalar.h:
##########
@@ -1807,5 +1807,46 @@ ARROW_EXPORT Result<Datum> NanosecondsBetween(const
Datum& left, const Datum& ri
/// \note API not yet finalized
ARROW_EXPORT Result<Datum> MapLookup(const Datum& map, MapLookupOptions
options,
ExecContext* ctx = NULLPTR);
+
+/// \brief Construct a hash value for each row of the input.
+///
+/// The result has the same length and shape as the input (Array in, Array out;
+/// ChunkedArray in, ChunkedArray out), but with element type UInt32. For a
nested
+/// input type (struct, list, map, etc.), each row's child values are combined
into a
+/// single hash for that row, recursively. A null input row produces a null
output row;
+/// within a struct, a null field makes that whole row null, while within a
list or map a
+/// null element does not (only the row's own validity matters there). Hash
values are not
+/// guaranteed to be stable across different versions of the library, and this
function
+/// does not currently take options, though these may be added in the future.
+///
+/// \param[in] input_array input data to hash
+/// \param[in] ctx function execution context, optional
+/// \return elementwise hash values
+///
+/// \since 26.0.0
+/// \note API not yet finalized
+ARROW_EXPORT
+Result<Datum> Hash32(const Datum& input_array, ExecContext* ctx = NULLPTR);
+
+/// \brief Construct a hash value for each row of the input.
+///
+/// The result has the same length and shape as the input (Array in, Array out;
+/// ChunkedArray in, ChunkedArray out), but with element type UInt64. For a
nested
Review Comment:
The C++ API docs describe only Array/ChunkedArray inputs, but these kernels
also accept Scalar input (and return a Scalar), as covered by
`TestScalarHash.ScalarInput`. Please document Scalar-in/Scalar-out in both
`Hash32` and `Hash64` docstrings.
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