How to save numpy masked array to file

Question

What is the most efficient way of saving a numpy masked array? Unfortunately numpy.save doesn't work:

import numpy as np
a = np.ma.zeros((500, 500))
np.save('test', a)

This gives a:

NotImplementedError: Not implemented yet, sorry...

One way seems to be using pickle, but that unfortunately is not very efficient (huge file sizes), and not platform-independent. Also, netcdf4 seems to work, but it has a large overhead just to save a simple array.

Anyone has had this problem before? I'm tempted just to do numpy.save of array.data and another for the mask.

Answer 1

The current accepted answer is somewhat obsolete, and badly inefficient if the array being stored is sparse (it relies on uncompressed pickling of the array).

A better way to save/load a masked array would be to use an npz file:

import numpy as np

# Saving masked array 'arr':
np.savez_compressed('test.npz', data=arr.data, mask=arr.mask)

# Loading array back
with np.load('test.npz') as npz:
    arr = np.ma.MaskedArray(**npz)

Answer 2

import numpy as np
a = np.ma.zeros((500, 500))
a.dump('test')

then read it with

a = np.load('test')