How can I save a matrix in a txt file and then open it again as a matrix in python?

Question

I tried this:

  import numpy as np
  import os

  outdir= "directory"

  a = np.array([[1,2,3],[1,2,3]])

  os.chdir(outdir)

  np.savetxt("Image.bin", a)

  f = open("directory/Image.bin")
  m = np.fromfile(f, dtype=np.uint16)
  print len(m)
  ma = np.array(np.reshape(m, (2,3)))

  print ma

But it returns this error message: "total size of new array must be unchanged"

I tried to change the dtype, but it dosen't work

Answer 1

You should use np.loadtxt : http://docs.scipy.org/doc/numpy/reference/generated/numpy.loadtxt.html

Try:

import numpy as np

a = np.array([[1,2,3],[1,2,3]])
np.savetxt("Image.bin", a)
m = np.loadtxt("Image.bin")

m now contains the same array as a .

Answer 2

numpy has built in functions for saving and loading arrays as binary files.

numpy.save('data.npy', data)

will create the file (it will append npy if you don't), and

data = numpy.load('data.npy')

will load it from the file. This is both faster and more space efficient than saving them as text files.