numpy boolean array with 1 bit entries

Question

Is there a way in numpy to create an array of booleans that uses just 1 bit for each entry?

The standard np.bool type is 1 byte, but this way I use 8 ti

Answer 1

To do this you can use numpy's native packbits and unpackbits. The first function is straight-forward to use, but to reconstruct you will need additional manipulations. Here is an example:

import numpy as np
# original boolean array
A1 = np.array([
    [0, 1, 1, 0, 1],
    [0, 0, 1, 1, 1],
    [1, 1, 1, 1, 1],
], dtype=np.bool)

# packed data
A2 = np.packbits(A1, axis=None)

# checking the size
print(len(A1.tostring())) # 15 bytes
print(len(A2.tostring())) #  2 bytes (ceil(15/8))

# reconstructing from packed data. You need to resize and reshape
A3 = np.unpackbits(A2, axis=None)[:A1.size].reshape(A1.shape).astype(np.bool)

# and the arrays are equal
print(np.array_equal(A1, A3)) # True