How to change numpy array int values to chars?

Question

I am trying to change the value of a numpy array with generated values to char :

np_array = np.random.randint(0, 255, 5)
for i in range(256):
    np_array[sample_data == i] = chr(i)

However it gives me the error :

ValueError: invalid literal for int() with base 10: 'x00'

I’d assume that np.array is flexible like a list able to hold other values is that not case? does it work like a real array? do I need to create another variable that is a char, how do I do that without having a loop?

Asked By: fishbowl1

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Source

Answer 1

You can use numpy.ndarray.view method to view the integers as unicode characters.

Note:
Since you are generating integers without specifying their dtype – it is selected automatically. It can be different on different systems, and you have to set it explicitly before calling .view:

np_array = np_array.astype('uint32')

Alternatively, you can simply specify it when generating the integers, and then you won’t need to change it in the future:

np_array = np.random.randint(0, 255, 5, dtype='uint32')

To convert integers to unicode characters you can use either ‘U1’: 4 bytes, or ‘U2’: 8 bytes.

Here I’m setting the necessary dtype just to be explicit:

np_array = np_array.astype('uint32').view('U1')
# or
np_array = np_array.astype('uint64').view('U2')

Credit:
https://gist.github.com/tkf/2276773

Answered By: Vladimir Fokow

How to change numpy array int values to chars?

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