npyio – codeberg.org/sbinet/npyio Index | Examples | Files | Directories

package npyio

import "codeberg.org/sbinet/npyio"

Package npyio provides read/write access to files following the NumPy data file format: 

https://numpy.org/neps/nep-0001-npy-format.html

Supported types

npyio supports r/w of scalars, arrays, slices and gonum/mat.Dense. Supported scalars are:

Reading

Reading from a NumPy data file can be performed like so: 

f, err := os.Open("data.npy")
var m mat.Dense
err = npyio.Read(f, &m)
fmt.Printf("data = %v\n", mat.Formatted(&m, mat.Prefix("       "))))

npyio can also read data directly into slices, arrays or scalars, provided the on-disk data type and the provided one match.

Example: 

var data []float64
err = npyio.Read(f, &data)

var data uint64
err = npyio.Read(f, &data)

Writing

Writing into a NumPy data file can be done like so: 

f, err := os.Create("data.npy")
var m mat.Dense = ...
err = npyio.Write(f, m)

Scalars, arrays and slices are also supported: 

var data []float64 = ...
err = npyio.Write(f, data)

var data int64 = 42
err = npyio.Write(f, data)

var data [42]complex128 = ...
err = npyio.Write(f, data)
Example (PartialRead)

Code:play  

package main

import (
	"fmt"
	"log"
	"os"

	"codeberg.org/sbinet/npyio"
)

func main() {
	out, err := os.Create("data.npy")
	if err != nil {
		log.Fatal(err)
	}
	defer out.Close()

	f := []float64{0, 1, 2, 3, 4, 5}
	fmt.Printf("-- original data --\n")
	fmt.Printf("data = %v\n", f)
	err = npyio.Write(out, f)
	if err != nil {
		log.Fatalf("error writing data: %v\n", err)
	}
	err = out.Close()
	if err != nil {
		log.Fatal(err)
	}

	in, err := os.Open("data.npy")
	if err != nil {
		log.Fatal(err)
	}
	defer in.Close()
	r, err := npyio.NewReader(in)
	if err != nil {
		log.Fatal(err)
	}

	data := make([]float64, 3)
	err = r.Read(&data)
	if err != nil {
		log.Fatalf("error reading data: %v\n", err)
	}

	fmt.Printf("-- partial data read back --\n")
	fmt.Printf("data = %v\n", data)

	err = r.Read(&data)
	if err != nil {
		log.Fatalf("error reading data: %v\n", err)
	}

	fmt.Printf("-- rest of data read back --\n")
	fmt.Printf("data = %v\n", data)

}

Output:

-- original data --
data = [0 1 2 3 4 5]
-- partial data read back --
data = [0 1 2]
-- rest of data read back --
data = [3 4 5]

Index

Examples

Variables 

var (
	// ErrInvalidNumPyFormat is the error returned by NewReader when
	// the underlying io.Reader is not a valid or recognized NumPy data
	// file format.
	ErrInvalidNumPyFormat = npy.ErrInvalidNumPyFormat

	// ErrTypeMismatch is the error returned by Reader when the on-disk
	// data type and the user provided one do NOT match.
	ErrTypeMismatch = npy.ErrTypeMismatch

	// ErrInvalidType is the error returned by Reader and Writer when
	// confronted with a type that is not supported or can not be
	// reliably (de)serialized.
	ErrInvalidType = npy.ErrInvalidType

	// Magic header present at the start of a NumPy data file format.
	// See https://numpy.org/neps/nep-0001-npy-format.html
	Magic = npy.Magic
)

Functions

func Dump 

func Dump(o io.Writer, r io.ReaderAt) error

Dump dumps the content of the provided reader to the writer, in a human readable format

func Read 

func Read(r io.Reader, ptr interface{}) error

Read reads the data from the r NumPy data file io.Reader, into the provided pointed at value ptr. Read returns an error if the on-disk data type and the one provided don't match.

If a *mat.Dense matrix is passed to Read, the numpy-array data is loaded into the Dense matrix, honouring Fortran/C-order and dimensions/shape parameters.

Only numpy-arrays with up to 2 dimensions are supported. Only numpy-arrays with elements convertible to float64 are supported.

Example

Code:play  

package main

import (
	"bytes"
	"fmt"
	"log"

	"gonum.org/v1/gonum/mat"

	"codeberg.org/sbinet/npyio"
)

func main() {
	m := mat.NewDense(2, 3, []float64{0, 1, 2, 3, 4, 5})
	fmt.Printf("-- original data --\n")
	fmt.Printf("data = %v\n", mat.Formatted(m, mat.Prefix("       ")))
	buf := new(bytes.Buffer)

	err := npyio.Write(buf, m)
	if err != nil {
		log.Fatalf("error writing data: %v\n", err)
	}

	// modify original data
	m.Set(0, 0, 6)

	var data mat.Dense
	err = npyio.Read(buf, &data)
	if err != nil {
		log.Fatalf("error reading data: %v\n", err)
	}

	fmt.Printf("-- data read back --\n")
	fmt.Printf("data = %v\n", mat.Formatted(&data, mat.Prefix("       ")))

	fmt.Printf("-- modified original data --\n")
	fmt.Printf("data = %v\n", mat.Formatted(m, mat.Prefix("       ")))

}

Output:

-- original data --
data = ⎡0  1  2⎤
       ⎣3  4  5⎦
-- data read back --
data = ⎡0  1  2⎤
       ⎣3  4  5⎦
-- modified original data --
data = ⎡6  1  2⎤
       ⎣3  4  5⎦

func TypeFrom 

func TypeFrom(dtype string) reflect.Type

TypeFrom returns the reflect.Type corresponding to the numpy-dtype string, if any.

func Write 

func Write(w io.Writer, val interface{}) error

Write writes 'val' into 'w' in the NumPy data format.

The data-array will always be written out in C-order (row-major).

Example

Code:play  

package main

import (
	"bytes"
	"fmt"
	"log"

	"gonum.org/v1/gonum/mat"

	"codeberg.org/sbinet/npyio"
)

func main() {
	m := mat.NewDense(2, 3, []float64{0, 1, 2, 3, 4, 5})
	fmt.Printf("-- original data --\n")
	fmt.Printf("data = %v\n", mat.Formatted(m, mat.Prefix("       ")))
	buf := new(bytes.Buffer)

	err := npyio.Write(buf, m)
	if err != nil {
		log.Fatalf("error writing data: %v\n", err)
	}

	// modify original data
	m.Set(0, 0, 6)

	var data mat.Dense
	err = npyio.Read(buf, &data)
	if err != nil {
		log.Fatalf("error reading data: %v\n", err)
	}

	fmt.Printf("-- data read back --\n")
	fmt.Printf("data = %v\n", mat.Formatted(&data, mat.Prefix("       ")))

	fmt.Printf("-- modified original data --\n")
	fmt.Printf("data = %v\n", mat.Formatted(m, mat.Prefix("       ")))

}

Output:

-- original data --
data = ⎡0  1  2⎤
       ⎣3  4  5⎦
-- data read back --
data = ⎡0  1  2⎤
       ⎣3  4  5⎦
-- modified original data --
data = ⎡6  1  2⎤
       ⎣3  4  5⎦

Types 

type Header = npy.Header

Header describes the data content of a NumPy data file.

type Reader 

type Reader = npy.Reader

Reader reads data from a NumPy data file.

func NewReader 

func NewReader(r io.Reader) (*Reader, error)

NewReader creates a new NumPy data file format reader.

Source Files

dump.go npyio.go

Directories

PathSynopsis
cmd
cmd/npyio-ls
npyPackage npy provides read/write access to files following the NumPy data file format:
npy/float16
npzPackage npz provides read/write access to files with compressed NumPy data file format:
Version
v0.10.0 (latest)
Published
Mar 4, 2025
Platform
linux/amd64
Imports
9 packages
Last checked
14 hours ago –

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