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feather.h
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139 lines (108 loc) · 3.99 KB
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// 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.
// Public API for the "Feather" file format, originally created at
// http://github.com/wesm/feather
#ifndef ARROW_IPC_FEATHER_H
#define ARROW_IPC_FEATHER_H
#include <cstdint>
#include <memory>
#include <string>
#include "arrow/util/visibility.h"
namespace arrow {
class Array;
class Column;
class Status;
namespace io {
class OutputStream;
class RandomAccessFile;
} // namespace io
namespace ipc {
namespace feather {
static constexpr const int kFeatherVersion = 2;
// ----------------------------------------------------------------------
// Metadata accessor classes
/// \class TableReader
/// \brief An interface for reading columns from Feather files
class ARROW_EXPORT TableReader {
public:
TableReader();
~TableReader();
/// \brief Open a Feather file from a RandomAccessFile interface
///
/// \param[in] source a RandomAccessFile instance
/// \param[out] out the table reader
static Status Open(const std::shared_ptr<io::RandomAccessFile>& source,
std::unique_ptr<TableReader>* out);
/// \brief Optional table description
///
/// This does not return a const std::string& because a string has to be
/// copied from the flatbuffer to be able to return a non-flatbuffer type
std::string GetDescription() const;
/// \brief Return true if the table has a description field populated
bool HasDescription() const;
/// \brief Return the version number of the Feather file
int version() const;
/// \brief Return the number of rows in the file
int64_t num_rows() const;
/// \brief Return the number of columns in the file
int64_t num_columns() const;
std::string GetColumnName(int i) const;
/// \brief Read a column from the file as an arrow::Column.
///
/// \param[in] i the column index to read
/// \param[out] out the returned column
/// \return Status
///
/// This function is zero-copy if the file source supports zero-copy reads
Status GetColumn(int i, std::shared_ptr<Column>* out);
private:
class ARROW_NO_EXPORT TableReaderImpl;
std::unique_ptr<TableReaderImpl> impl_;
};
/// \class TableWriter
/// \brief Interface for writing Feather files
class ARROW_EXPORT TableWriter {
public:
~TableWriter();
/// \brief Create a new TableWriter that writes to an OutputStream
/// \param[in] stream an output stream
/// \param[out] out the returned table writer
/// \return Status
static Status Open(const std::shared_ptr<io::OutputStream>& stream,
std::unique_ptr<TableWriter>* out);
/// \brief Set the description field in the file metadata
void SetDescription(const std::string& desc);
/// \brief Set the number of rows in the file
void SetNumRows(int64_t num_rows);
/// \brief Append a column to the file
///
/// \param[in] name the column name
/// \param[in] values the column values as a contiguous arrow::Array
/// \return Status
Status Append(const std::string& name, const Array& values);
/// \brief Finalize the file by writing the file metadata and footer
/// \return Status
Status Finalize();
private:
TableWriter();
class ARROW_NO_EXPORT TableWriterImpl;
std::unique_ptr<TableWriterImpl> impl_;
};
} // namespace feather
} // namespace ipc
} // namespace arrow
#endif // ARROW_IPC_FEATHER_H