Example of applying a group-by operation with arrow-c++

example.cc

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// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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// specific language governing permissions and limitations
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#include <arrow/io/api.h>
#include <arrow/array/builder_primitive.h>
#include <arrow/array/builder_binary.h>
#include <arrow/compute/api.h>
#include <arrow/compute/exec/exec_plan.h>
#include <arrow/compute/exec/options.h>
#include <arrow/result.h>
#include <arrow/status.h>
#include <arrow/table.h>
#include <parquet/arrow/writer.h>

#include <iostream>

using arrow::Result;
using arrow::Status;

namespace
{

  static constexpr int32_t kNumVals = 10000;

  Result<std::shared_ptr<arrow::Array>> ValuesArray()
  {
    arrow::Int32Builder builder;
    ARROW_RETURN_NOT_OK(builder.Reserve(kNumVals));
    for (int32_t i = 0; i < kNumVals; i++)
    {
      ARROW_RETURN_NOT_OK(builder.Append(i));
    }
    return builder.Finish();
  }

  Result<std::shared_ptr<arrow::Array>> KeysArray()
  {
    arrow::StringBuilder builder;
    ARROW_RETURN_NOT_OK(builder.Reserve(kNumVals));
    for (int32_t i = 0; i < kNumVals; i++)
    {
      if (i % 2 == 0)
      {
        ARROW_RETURN_NOT_OK(builder.Append("A"));
      }
      else
      {
        ARROW_RETURN_NOT_OK(builder.Append("B"));
      }
    }
    return builder.Finish();
  }

  Result<std::shared_ptr<arrow::Table>> MakeSampleTable()
  {
    std::shared_ptr<arrow::Schema> schema = arrow::schema({arrow::field("keys", arrow::utf8()), arrow::field("values", arrow::int32())});
    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Array> keys, KeysArray());
    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Array> values, ValuesArray());
    return arrow::Table::Make(std::move(schema), {std::move(keys), std::move(values)}, kNumVals);
  }

  Status UsingAPlan()
  {
    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Table> sample_table, MakeSampleTable());

    arrow::compute::Aggregate aggregate;
    aggregate.function = "hash_sum";                             // The function to apply
    aggregate.name = "SUM OF VALUES";                            // The default name of the output column
    aggregate.options = nullptr;                                 // Custom options (e.g. how to handle null)
    aggregate.target = std::vector<arrow::FieldRef>({"values"}); // Which field to aggregate.  Some aggregate functions (e.g. covariance)
                                                                 // may require targetting multiple fields
    arrow::compute::Declaration plan = arrow::compute::Declaration::Sequence({{"table_source", arrow::compute::TableSourceNodeOptions(std::move(sample_table))},
                                                                              {"aggregate", arrow::compute::AggregateNodeOptions(/*aggregates=*/{aggregate}, /*keys=*/{"keys"})}});

    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Table> grouped, arrow::compute::DeclarationToTable(std::move(plan)));
    std::cout << grouped->ToString() << std::endl;
    return Status::OK();
  }

  Status UsingConvenience()
  {
    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Table> sample_table, MakeSampleTable());

    arrow::compute::Aggregate aggregate;
    aggregate.function = "hash_sum";                             // The function to apply
    aggregate.name = "SUM OF VALUES";                            // The default name of the output column
    aggregate.options = nullptr;                                 // Custom options (e.g. how to handle null)
    aggregate.target = std::vector<arrow::FieldRef>({"values"}); // Which field to aggregate.  Some aggregate functions (e.g. covariance)
                                                                 // may require targetting multiple fields

    ARROW_ASSIGN_OR_RAISE(std::shared_ptr<arrow::Table> grouped,
                          arrow::compute::TableGroupBy(std::move(sample_table), {std::move(aggregate)}, {"keys"}));
    std::cout << grouped->ToString() << std::endl;
    return Status::OK();
  }

} // namespace

int main()
{
  Status st = UsingAPlan();
  if (st.ok())
  {
    st = UsingConvenience();
  }
  if (!st.ok())
  {
    std::cerr << st << std::endl;
    return 1;
  }
  return 0;
}