libnpy

libnpy is a simple C++ library for reading and writing of numpy's .npy files.

Refer to format.py for a detailed description of the .npy format.

This libraries primary purpose is writing numerical data easily and efficiently into the .npy format. It also allows reading .npy files, although only a very limited subset of data types are supported.

Features

• Writing C++ vectors (std::vector) to .npy files
• Reading (some) simple .npy files into C++ vectors

Supported data types and mapping

Only scalar numeric data types are supported. There is no natural way to represent more complex objects and parsing the header becomes tremendously more complex. Supported types:

• unsigned integer
• signed integer
• floating point
• complex floating point (std::complex, ...)

Usage

libnpy is a header only library. You only need to download npy.hpp into your include path. Neither special compiler flags nor a specific build system are required.

Optional: If you use meson, you can use the provided meson.build file to declare the dependency on libnpy.

Reading data:

#include "npy.hpp"
#include <vector>
#include <string>

int main() {
  std::vector<unsigned long> shape {};
  bool fortran_order;
  std::vector<double> data;
  
  const std::string path {"data.npy"};
  npy::LoadArrayFromNumpy(path, shape, fortran_order, data);
}

Writing data:

#include "npy.hpp"
#include <vector>
#include <string>

int main() {
  const std::vector<long unsigned> shape{2, 3};
  const bool fortran_order{false};
  const std::string path{"out.npy"};

  const std::vector<double> data1{1, 2, 3, 4, 5, 6};
  npy::SaveArrayAsNumpy(path, fortran_order, shape.size(), shape.data(), data1);
}

See test/ for further examples. C++11 is required. If you use g++, use -std=c++11.

Tests

The tests can be build with meson>=0.55 and depend on catch2.

cd tests
meson setup builddir
meson test -Cbuilddir

Known limitations

1. Only a few data types are supported.

2. The numpy header is a literal Python dictionary and the Python syntax is very permissive. libnpy's parser was only tested with numpy's implemenation of the .npy format.

Contributing

Feel free to send me a pull request, open an issue, or contact me directly.

License

The project is licensed under the MIT license