bkietz commented on a change in pull request #9621:
URL: https://github.com/apache/arrow/pull/9621#discussion_r599006347
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File path: cpp/src/arrow/compute/api_aggregate.h
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@@ -306,5 +306,100 @@ Result<Datum> TDigest(const Datum& value,
const TDigestOptions& options =
TDigestOptions::Defaults(),
ExecContext* ctx = NULLPTR);
+namespace internal {
+
+/// Internal use only: streaming group identifier.
+/// Consumes batches of keys and yields batches of the group ids.
+class ARROW_EXPORT Grouper {
+ public:
+ virtual ~Grouper() = default;
+
+ /// Construct a Grouper which receives the specified key types
+ static Result<std::unique_ptr<Grouper>> Make(const std::vector<ValueDescr>&
descrs,
+ ExecContext* ctx =
default_exec_context());
+
+ /// Consume a batch of keys, producing the corresponding group ids as an
integer array.
+ virtual Result<Datum> Consume(const ExecBatch& batch) = 0;
+
+ /// Get current unique keys. May be called multiple times.
+ virtual Result<ExecBatch> GetUniques() = 0;
+
+ /// Get the current number of groups.
Review comment:
The number of key(column)s is fixed throughout the lifetime of the
Grouper. The number of groups is incremented each time a unique row of keys is
encountered.
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