cyb70289 commented on a change in pull request #7963:
URL: https://github.com/apache/arrow/pull/7963#discussion_r474658427
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File path: cpp/src/arrow/compute/kernels/aggregate_mode.cc
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@@ -69,28 +72,83 @@ struct ModeState {
std::unordered_map<T, int64_t> value_counts{};
};
+// Use array to count small integers(bool, int8, uint8), improves performance
2x ~ 6x
+template <typename ArrowType>
+struct ModeState<ArrowType, enable_if_t<(sizeof(typename ArrowType::c_type) ==
1)>> {
+ using ThisType = ModeState<ArrowType>;
+ using T = typename ArrowType::c_type;
+ using Limits = std::numeric_limits<T>;
+
+ ModeState() : value_counts(Limits::max() - Limits::min() + 1) {}
+
+ void MergeFrom(const ThisType& state) {
+ std::transform(this->value_counts.cbegin(), this->value_counts.cend(),
+ state.value_counts.cbegin(), this->value_counts.begin(),
+ std::plus<int64_t>{});
+ }
+
+ void MergeOne(T value) { ++this->value_counts[value - Limits::min()]; }
+
+ std::pair<T, int64_t> Finalize() {
+ T mode = Limits::min();
+ int64_t count = 0;
+
+ for (int i = 0; i <= Limits::max() - Limits::min(); ++i) {
+ T this_value = static_cast<T>(i + Limits::min());
+ int64_t this_count = this->value_counts[i];
+ if (this_count > count || (this_count == count && this_value < mode)) {
+ count = this_count;
+ mode = this_value;
+ }
+ }
+ return std::make_pair(mode, count);
+ }
+
+ std::vector<int64_t> value_counts;
+};
+
+// read raw_values[] directly improves performance ~15%
Review comment:
Agreed. Will remove it.
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