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)
works but only for 8 bit values ..if the numpy is 9 or more elements it generates 2 or more 8bit values. Another option would be to return a string of 0|1 ...
What I currently do is :
ba = bitarray()
ba.pack(b.astype(np.bool).tostring())
#convert from bitarray 0|1 to integer
result = int( ba.to01(), 2 )
which is ugly !!!
One way would be using dot-product with 2-powered range array -
b.dot(2**np.arange(b.size)[::-1])
Sample run -
In [95]: b = np.array([1,0,1,0,0,0,0,0,1,0,1])
In [96]: b.dot(2**np.arange(b.size)[::-1])
Out[96]: 1285
Alternatively, we could use bitwise left-shift operator to create the range array and thus get the desired output, like so -
b.dot(1 << np.arange(b.size)[::-1])
If timings are of interest -
In [148]: b = np.random.randint(0,2,(50))
In [149]: %timeit b.dot(2**np.arange(b.size)[::-1])
100000 loops, best of 3: 13.1 µs per loop
In [150]: %timeit b.dot(1 << np.arange(b.size)[::-1])
100000 loops, best of 3: 7.92 µs per loop
Reverse process
To retrieve back the binary array, use np.binary_repr alongwith np.fromstring -
In [96]: b = np.array([1,0,1,0,0,0,0,0,1,0,1])
In [97]: num = b.dot(2**np.arange(b.size)[::-1]) # integer
In [98]: np.fromstring(np.binary_repr(num), dtype='S1').astype(int)
Out[98]: array([1, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1])