[GitHub] [arrow] lidavidm commented on a change in pull request #10890: ARROW-13575: [C++] Add hash_product kernel

[GitBox <gi...@apache.org>]

lidavidm commented on a change in pull request #10890:
URL: https://github.com/apache/arrow/pull/10890#discussion_r684235385



##########
File path: cpp/src/arrow/compute/kernels/hash_aggregate.cc
##########
@@ -1011,6 +1011,108 @@ struct GroupedSumFactory {
   InputType argument_type;
 };
 
+// ----------------------------------------------------------------------
+// Product implementation
+
+template <typename Type>
+struct GroupedProductImpl : public GroupedAggregator {
+  using AccType = typename FindAccumulatorType<Type>::Type;
+  using ProductType = typename TypeTraits<AccType>::CType;
+
+  Status Init(ExecContext* ctx, const FunctionOptions*) override {
+    pool_ = ctx->memory_pool();
+    products_ = TypedBufferBuilder<ProductType>(pool_);
+    valid_ = TypedBufferBuilder<bool>(pool_);
+    out_type_ = TypeTraits<AccType>::type_singleton();
+    return Status::OK();
+  }
+
+  Status Resize(int64_t new_num_groups) override {
+    auto added_groups = new_num_groups - num_groups_;
+    num_groups_ = new_num_groups;
+    RETURN_NOT_OK(products_.Append(added_groups * sizeof(AccType), 1));
+    RETURN_NOT_OK(valid_.Append(added_groups, false));
+    return Status::OK();
+  }
+
+  Status Consume(const ExecBatch& batch) override {
+    ProductType* products = products_.mutable_data();
+    auto valid = valid_.mutable_data();
+
+    auto g = batch[1].array()->GetValues<uint32_t>(1);
+    VisitArrayDataInline<Type>(
+        *batch[0].array(),
+        [&](typename TypeTraits<Type>::CType value) {
+          products[*g] *= value;

Review comment:
       Ah fair point. Updated to check for overflow for integers.




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