CODEWITHSUNDEEP
pythonarraysnumpy
Alheana
Alheana

Reputation: 159

Numpy astype rounding to wrong value

So I am trying to turn my float numpy array to integers. But when I do so:

array.astype(np.uint64)

it changes this array:

[ 550.  514.  451.  494.  490.  500.  ...]

to this one:

[549 513 450 493 489 499 ... ]

So, I was wondering if any of you had an idea of why this is? I have to get np.uint64 as output for the code I am using next.

Thank you in advance.

Upvotes: 14

Views: 10793

Answers (1)

user6655984
user6655984

Reputation:

As was said in comments, casting to integers does not round, it simply truncates the non-integer part. A float that appears as 550. in console output may actually be 549.999999999 which will be truncated to 549. Use rounding before typecasting. An example: 

>>> a = np.array([5, 6, 7], dtype=float) - 1e-12
>>> a
array([ 5.,  6.,  7.])
>>> a.astype(np.uint64)
array([4, 5, 6], dtype=uint64)
>>> np.around(a).astype(np.uint64)
array([5, 6, 7], dtype=uint64)

Upvotes: 23

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