python: convert ascii character to boolean array

Question

I have a character. I want to represent its ascii value as a numpy array of booleans. This works, but seems contorted. Is there a better way?

bin_str = bin(ord(mychar))
bool_array = array([int(x)>0 for x in list(bin_str[2:])], dtype=bool)

for

mychar = 'd'

the desired resulting value for bool_array is

array([ True,  True, False, False,  True, False, False], dtype=bool)

That looks like the wrong tool (meant for interactions with binary files, not conversions within python code), and even if it would do what I want, importing a c-based module seems like a worse solution than what I already have. — persephani
– persephani, Commented Jul 19, 2013 at 10:58

Jaime · Accepted Answer · 2013-07-19 21:59:31Z

1

You can extract the bits from a uint8 array directly using np.unpackbits:

np.unpackbits(np.array(ord(mychar), dtype=np.uint8))

EDIT: To get only the 7 relevant bits in a boolean array:

np.unpackbits(np.array(ord(mychar), dtype=np.uint8)).astype(bool)[1:]

edited Jul 19, 2013 at 21:59

answered Jul 19, 2013 at 15:05

Jaime

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3 Comments

persephani Over a year ago

this does not exactly do what I want - it is an array of numbers, not booleans. to get the boolean result I want I need to do array([x>0 for x in np.unpackbits(np.array(ord(mychar), dtype=np.uint8))]). And still that's not quite right because it prepends a False to get the uint8 out of ascii's 7 bits.

persephani Over a year ago

though i didn't previously know about unpackbits, which looks useful for other problems, so thank you.

persephani Over a year ago

ah, thanks. that does look a little cleaner than @tiago 's solution.

tiago · Accepted Answer · 2013-07-19 14:42:57Z

0

This is more or less the same thing:

>>> import numpy as np
>>> mychar = 'd'
>>> np.array(list(np.binary_repr(ord(mychar), width=4))).astype('bool')
array([ True,  True, False, False,  True, False, False], dtype=bool)

Is it less contorted?

answered Jul 19, 2013 at 14:42

tiago

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3 Comments

persephani Over a year ago

it's easier for me to read, and gives the right result, so, yes. thank you.

persephani Over a year ago

also, the width=4 argument is unnecessary, so np.array(list(np.binary_repr(ord(mychar)))).astype('bool') works

persephani Over a year ago

ok, this is closest to my eventual solution, which doesn't use any other numpy functions aside from array itself: np.array(list(bin(ord('d'))))[2:].astype(bool)

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