cpp/examples/arrow/compute_and_write_csv_example.cc

// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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 <arrow/api.h>
#include <arrow/compute/api.h>
#include <arrow/csv/api.h>
#include <arrow/csv/writer.h>
#include <arrow/io/api.h>
#include <arrow/result.h>
#include <arrow/status.h>

#include <iostream>
#include <vector>

// Many operations in Apache Arrow operate on
// columns of data, and the columns of data are
// assembled into a table. In this example, we
// examine how to compare two arrays which are
// combined to form a table that is then written
// out to a CSV file.
//
// To run this example you can use
// ./compute_and_write_csv_example
//
// the program will write the files into
// compute_and_write_output.csv
// in the current directory

arrow::Status RunMain(int argc, char** argv) {
  // Make Arrays
  arrow::NumericBuilder<arrow::Int64Type> int64_builder;
  arrow::BooleanBuilder boolean_builder;

  // Make place for 8 values in total
  ARROW_RETURN_NOT_OK(int64_builder.Resize(8));
  ARROW_RETURN_NOT_OK(boolean_builder.Resize(8));

  // Bulk append the given values
  std::vector<int64_t> int64_values = {1, 2, 3, 4, 5, 6, 7, 8};
  ARROW_RETURN_NOT_OK(int64_builder.AppendValues(int64_values));
  std::shared_ptr<arrow::Array> array_a;
  ARROW_RETURN_NOT_OK(int64_builder.Finish(&array_a));
  int64_builder.Reset();
  int64_values = {2, 5, 1, 3, 6, 2, 7, 4};
  std::shared_ptr<arrow::Array> array_b;
  ARROW_RETURN_NOT_OK(int64_builder.AppendValues(int64_values));
  ARROW_RETURN_NOT_OK(int64_builder.Finish(&array_b));

  // Cast the arrays to their actual types
  auto int64_array_a = std::static_pointer_cast<arrow::Int64Array>(array_a);
  auto int64_array_b = std::static_pointer_cast<arrow::Int64Array>(array_b);
  // Explicit comparison of values using a loop
  for (int64_t i = 0; i < 8; i++) {
    if ((!int64_array_a->IsNull(i)) && (!int64_array_b->IsNull(i))) {
      bool comparison_result = int64_array_a->Value(i) > int64_array_b->Value(i);
      boolean_builder.UnsafeAppend(comparison_result);
    } else {
      boolean_builder.UnsafeAppendNull();
    }
  }
  std::shared_ptr<arrow::Array> array_a_gt_b_self;
  ARROW_RETURN_NOT_OK(boolean_builder.Finish(&array_a_gt_b_self));
  std::cout << "Array explicitly compared" << std::endl;

  // Explicit comparison of values using a compute function
  ARROW_ASSIGN_OR_RAISE(arrow::Datum compared_datum,
                        arrow::compute::CallFunction("greater", {array_a, array_b}));
  auto array_a_gt_b_compute = compared_datum.make_array();
  std::cout << "Arrays compared using a compute function" << std::endl;

  // Create a table for the output
  auto schema =
      arrow::schema({arrow::field("a", arrow::int64()), arrow::field("b", arrow::int64()),
                     arrow::field("a>b? (self written)", arrow::boolean()),
                     arrow::field("a>b? (arrow)", arrow::boolean())});
  std::shared_ptr<arrow::Table> my_table = arrow::Table::Make(
      schema, {array_a, array_b, array_a_gt_b_self, array_a_gt_b_compute});

  std::cout << "Table created" << std::endl;

  // Write table to CSV file
  auto csv_filename = "compute_and_write_output.csv";
  ARROW_ASSIGN_OR_RAISE(auto outstream, arrow::io::FileOutputStream::Open(csv_filename));

  std::cout << "Writing CSV file" << std::endl;
  ARROW_RETURN_NOT_OK(arrow::csv::WriteCSV(
      *my_table, arrow::csv::WriteOptions::Defaults(), outstream.get()));

  return arrow::Status::OK();
}

int main(int argc, char** argv) {
  arrow::Status status = RunMain(argc, argv);
  if (!status.ok()) {
    std::cerr << status.ToString() << std::endl;
    return EXIT_FAILURE;
  }
  return EXIT_SUCCESS;
}