Convert binary (0|1) numpy to integer or binary-string?

Question

Is there a shortcut to Convert binary (0|1) numpy array to integer or binary-string ? F.e.

b = np.array([0,0,0,0,0,1,0,1])   
  => b is 5

np.packbits(b)
         


        

Answer 1

Using numpy for conversion limits you to 64-bit signed binary results. If you really want to use numpy and the 64-bit limit works for you a faster implementation using numpy is:

import numpy as np
def bin2int(bits):
    return np.right_shift(np.packbits(bits, -1), bits.size).squeeze()

Since normally if you are using numpy you care about speed then the fastest implementation for > 64-bit results is:

import gmpy2
def bin2int(bits):
    return gmpy2.pack(list(bits[::-1]), 1)

If you don't want to grab a dependency on gmpy2 this is a little slower but has no dependencies and supports > 64-bit results:

def bin2int(bits):
    total = 0
    for shift, j in enumerate(bits[::-1]):
        if j:
            total += 1 << shift
    return total

The observant will note some similarities in the last version to other Answers to this question with the main difference being the use of the << operator instead of **, in my testing this led to a significant improvement in speed.