Add support for collect_list Spark aggregate function

velox/docs/functions/spark/aggregate.rst

@@ -53,6 +53,11 @@ General Aggregate Functions
 
     ``hash`` cannot be null.
 
+.. spark:function:: collect_list(x) -> array<[same as x]>
+
+    Returns an array created from the input ``x`` elements. Ignores null
+    inputs, and returns an empty array when all inputs are null.
+
 .. spark:function:: first(x) -> x
 
     Returns the first value of `x`.

velox/functions/sparksql/aggregates/CMakeLists.txt

@@ -17,6 +17,7 @@ add_library(
   BitwiseXorAggregate.cpp
   BloomFilterAggAggregate.cpp
   CentralMomentsAggregate.cpp
+  CollectListAggregate.cpp
   FirstLastAggregate.cpp
   MinMaxByAggregate.cpp
   Register.cpp

velox/functions/sparksql/aggregates/CollectListAggregate.cpp

@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "velox/functions/sparksql/aggregates/CollectListAggregate.h"
+
+#include "velox/exec/SimpleAggregateAdapter.h"
+#include "velox/functions/lib/aggregates/ValueList.h"
+
+using namespace facebook::velox::aggregate;
+using namespace facebook::velox::exec;
+
+namespace facebook::velox::functions::aggregate::sparksql {
+namespace {
+class CollectListAggregate {
+ public:
+  using InputType = Row<Generic<T1>>;
+
+  using IntermediateType = Array<Generic<T1>>;
+
+  using OutputType = Array<Generic<T1>>;
+
+  /// In Spark, when all inputs are null, the output is an empty array instead
+  /// of null. Therefore, in the writeIntermediateResult and writeFinalResult,
+  /// we still need to output the empty element_ when the group is null. This
+  /// behavior can only be achieved when the default-null behavior is disabled.
+  static constexpr bool default_null_behavior_ = false;
+
+  static bool toIntermediate(
+      exec::out_type<Array<Generic<T1>>>& out,
+      exec::optional_arg_type<Generic<T1>> in) {
+    if (in.has_value()) {
+      out.add_item().copy_from(in.value());
+      return true;
+    }
+    return false;
+  }
+
+  struct AccumulatorType {
+    ValueList elements_;
+
+    explicit AccumulatorType(HashStringAllocator* /*allocator*/)
+        : elements_{} {}
+
+    static constexpr bool is_fixed_size_ = false;
+
+    bool addInput(
+        HashStringAllocator* allocator,
+        exec::optional_arg_type<Generic<T1>> data) {
+      if (data.has_value()) {
+        elements_.appendValue(data, allocator);
+        return true;
+      }
+      return false;
+    }
+
+    bool combine(
+        HashStringAllocator* allocator,
+        exec::optional_arg_type<IntermediateType> other) {
+      if (!other.has_value()) {
+        return false;
+      }
+      for (auto element : other.value()) {
+        elements_.appendValue(element, allocator);
+      }
+      return true;
+    }
+
+    bool writeIntermediateResult(
+        bool /*nonNullGroup*/,
+        exec::out_type<IntermediateType>& out) {
+      // If the group's accumulator is null, the corresponding intermediate
+      // result is an empty array.
+      copyValueListToArrayWriter(out, elements_);
+      return true;
+    }
+
+    bool writeFinalResult(
+        bool /*nonNullGroup*/,
+        exec::out_type<OutputType>& out) {
+      // If the group's accumulator is null, the corresponding result is an
+      // empty array.
+      copyValueListToArrayWriter(out, elements_);
+      return true;
+    }
+
+    void destroy(HashStringAllocator* allocator) {
+      elements_.free(allocator);
+    }
+  };
+};
+
+AggregateRegistrationResult registerCollectList(
+    const std::string& name,
+    bool withCompanionFunctions,
+    bool overwrite) {
+  std::vector<std::shared_ptr<exec::AggregateFunctionSignature>> signatures{
+      exec::AggregateFunctionSignatureBuilder()
+          .typeVariable("E")
+          .returnType("array(E)")
+          .intermediateType("array(E)")
+          .argumentType("E")
+          .build()};
+  return exec::registerAggregateFunction(
+      name,
+      std::move(signatures),
+      [name](
+          core::AggregationNode::Step /*step*/,
+          const std::vector<TypePtr>& argTypes,
+          const TypePtr& resultType,
+          const core::QueryConfig& /*config*/)
+          -> std::unique_ptr<exec::Aggregate> {
+        VELOX_CHECK_EQ(
+            argTypes.size(), 1, "{} takes at most one argument", name);
+        return std::make_unique<SimpleAggregateAdapter<CollectListAggregate>>(
+            resultType);
+      },
+      withCompanionFunctions,
+      overwrite);
+}
+} // namespace
+
+void registerCollectListAggregate(
+    const std::string& prefix,
+    bool withCompanionFunctions,
+    bool overwrite) {
+  registerCollectList(
+      prefix + "collect_list", withCompanionFunctions, overwrite);
+}
+} // namespace facebook::velox::functions::aggregate::sparksql

velox/functions/sparksql/aggregates/CollectListAggregate.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace facebook::velox::functions::aggregate::sparksql {
+
+void registerCollectListAggregate(
+    const std::string& prefix,
+    bool withCompanionFunctions,
+    bool overwrite);
+
+} // namespace facebook::velox::functions::aggregate::sparksql

velox/functions/sparksql/aggregates/Register.cpp

@@ -20,6 +20,7 @@
 #include "velox/functions/sparksql/aggregates/BitwiseXorAggregate.h"
 #include "velox/functions/sparksql/aggregates/BloomFilterAggAggregate.h"
 #include "velox/functions/sparksql/aggregates/CentralMomentsAggregate.h"
+#include "velox/functions/sparksql/aggregates/CollectListAggregate.h"
 #include "velox/functions/sparksql/aggregates/SumAggregate.h"
 
 namespace facebook::velox::functions::aggregate::sparksql {
@@ -45,5 +46,6 @@ void registerAggregateFunctions(
   registerAverage(prefix + "avg", withCompanionFunctions, overwrite);
   registerSum(prefix + "sum", withCompanionFunctions, overwrite);
   registerCentralMomentsAggregate(prefix, withCompanionFunctions, overwrite);
+  registerCollectListAggregate(prefix, withCompanionFunctions, overwrite);
 }
 } // namespace facebook::velox::functions::aggregate::sparksql

velox/functions/sparksql/aggregates/tests/CMakeLists.txt

@@ -18,6 +18,7 @@ add_executable(
   BitwiseXorAggregationTest.cpp
   BloomFilterAggAggregateTest.cpp
   CentralMomentsAggregationTest.cpp
+  CollectListAggregateTest.cpp
   FirstAggregateTest.cpp
   LastAggregateTest.cpp
   Main.cpp

velox/functions/sparksql/aggregates/tests/CollectListAggregateTest.cpp

@@ -0,0 +1,127 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "velox/functions/lib/aggregates/tests/utils/AggregationTestBase.h"
+#include "velox/functions/sparksql/aggregates/Register.h"
+
+using namespace facebook::velox::functions::aggregate::test;
+
+namespace facebook::velox::functions::aggregate::sparksql::test {
+
+namespace {
+
+class CollectListAggregateTest : public AggregationTestBase {
+ protected:
+  void SetUp() override {
+    AggregationTestBase::SetUp();
+    registerAggregateFunctions("spark_");
+  }
+};
+
+TEST_F(CollectListAggregateTest, groupBy) {
+  std::vector<RowVectorPtr> batches;
+  // Creating 3 batches of input data.
+  // 0: {0, null} {0, 1}    {0, 2}
+  // 1: {1, 1}    {1, null} {1, 3}
+  // 2: {2, 2}    {2, 3}    {2, null}
+  // 3: {3, 3}    {3, 4}    {3, 5}
+  // 4: {4, 4}    {4, 5}    {4, 6}
+  for (auto i = 0; i < 3; i++) {
+    RowVectorPtr data = makeRowVector(
+        {makeFlatVector<int32_t>({0, 1, 2, 3, 4}),
+         makeFlatVector<int64_t>(
+             5,
+             [&i](const vector_size_t& row) { return i + row; },
+             [&i](const auto& row) { return i == row; })});
+    batches.push_back(data);
+  }
+
+  auto expected = makeRowVector(
+      {makeFlatVector<int32_t>({0, 1, 2, 3, 4}),
+       makeArrayVectorFromJson<int64_t>(
+           {"[1, 2]", "[1, 3]", "[2, 3]", "[3, 4, 5]", "[4, 5, 6]"})});
+
+  testAggregations(
+      batches,
+      {"c0"},
+      {"spark_collect_list(c1)"},
+      {"c0", "array_sort(a0)"},
+      {expected});
+  testAggregationsWithCompanion(
+      batches,
+      [](auto& /*builder*/) {},
+      {"c0"},
+      {"spark_collect_list(c1)"},
+      {{BIGINT()}},
+      {"c0", "array_sort(a0)"},
+      {expected},
+      {});
+}
+
+TEST_F(CollectListAggregateTest, global) {
+  auto data = makeRowVector({makeNullableFlatVector<int32_t>(
+      {std::nullopt, 1, 2, std::nullopt, 4, 5})});
+  auto expected =
+      makeRowVector({makeArrayVectorFromJson<int32_t>({"[1, 2, 4, 5]"})});
+
+  testAggregations(
+      {data}, {}, {"spark_collect_list(c0)"}, {"array_sort(a0)"}, {expected});
+  testAggregationsWithCompanion(
+      {data},
+      [](auto& /*builder*/) {},
+      {},
+      {"spark_collect_list(c0)"},
+      {{INTEGER()}},
+      {"array_sort(a0)"},
+      {expected});
+}
+
+TEST_F(CollectListAggregateTest, ignoreNulls) {
+  auto input = makeRowVector({makeNullableFlatVector<int32_t>(
+      {1, 2, std::nullopt, 4, std::nullopt, 6})});
+  // Spark will ignore all null values in the input.
+  auto expected =
+      makeRowVector({makeArrayVectorFromJson<int32_t>({"[1, 2, 4, 6]"})});
+  testAggregations(
+      {input}, {}, {"spark_collect_list(c0)"}, {"array_sort(a0)"}, {expected});
+  testAggregationsWithCompanion(
+      {input},
+      [](auto& /*builder*/) {},
+      {},
+      {"spark_collect_list(c0)"},
+      {{INTEGER()}},
+      {"array_sort(a0)"},
+      {expected},
+      {});
+}
+
+TEST_F(CollectListAggregateTest, allNullsInput) {
+  auto input = makeRowVector({makeAllNullFlatVector<int64_t>(100)});
+  // If all input data is null, Spark will output an empty array.
+  auto expected = makeRowVector({makeArrayVectorFromJson<int32_t>({"[]"})});
+  testAggregations({input}, {}, {"spark_collect_list(c0)"}, {expected});
+  testAggregationsWithCompanion(
+      {input},
+      [](auto& /*builder*/) {},
+      {},
+      {"spark_collect_list(c0)"},
+      {{BIGINT()}},
+      {},
+      {expected},
+      {});
+}
+} // namespace
+} // namespace facebook::velox::functions::aggregate::sparksql::test

velox/functions/sparksql/fuzzer/SparkAggregationFuzzerTest.cpp

@@ -71,7 +71,8 @@ int main(int argc, char** argv) {
           {"max_by", nullptr},
           {"min_by", nullptr},
           {"skewness", nullptr},
-          {"kurtosis", nullptr}};
+          {"kurtosis", nullptr},
+          {"collect_list", nullptr}};
 
   size_t initialSeed = FLAGS_seed == 0 ? std::time(nullptr) : FLAGS_seed;
   auto duckQueryRunner =
@@ -88,6 +89,9 @@ int main(int argc, char** argv) {
       // coefficient. Meanwhile, DuckDB employs the sample kurtosis calculation
       // formula. The results from the two methods are completely different.
       "kurtosis",
+      // When all data in a group are null, Spark returns an empty array while
+      // DuckDB returns null.
+      "collect_list",
   });
 
   using Runner = facebook::velox::exec::test::AggregationFuzzerRunner;