numpy TypeError：输入类型不支持 ufunc 'invert'，并且输入

Question

For the code below:

def makePrediction(mytheta, myx):
    # -----------------------------------------------------------------
    pr = sigmoid(np.dot(myx, mytheta))

    pr[pr < 0.5] =0
    pr[pr >= 0.5] = 1

    return pr

    # -----------------------------------------------------------------

# Compute the percentage of samples I got correct:
pos_correct = float(np.sum(makePrediction(theta,pos)))
neg_correct = float(np.sum(np.invert(makePrediction(theta,neg))))
tot = len(pos)+len(neg)
prcnt_correct = float(pos_correct+neg_correct)/tot
print("Fraction of training samples correctly predicted: %f." % prcnt_correct)

I get this error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-33-f0c91286cd02> in <module>()
     13 # Compute the percentage of samples I got correct:
     14 pos_correct = float(np.sum(makePrediction(theta,pos)))
---> 15 neg_correct = float(np.sum(np.invert(makePrediction(theta,neg))))
     16 tot = len(pos)+len(neg)
     17 prcnt_correct = float(pos_correct+neg_correct)/tot

TypeError: ufunc 'invert' not supported for the input types, and the inputs

Why is it happening and how can I fix it?

Answer 1

From the documentation :

Parameters:
x : array_like.
Only integer and boolean types are handled."

Your original array is floating point type (the return value of sigmoid() ); setting values in it to 0 and 1 won't change the type. You need to use astype(np.int) :

neg_correct = float(np.sum(np.invert(makePrediction(theta,neg).astype(np.int))))

should do it (untested).

---

Doing that, the float() cast you have also makes more sense. Though I would just remove the cast, and rely on Python doing the right thing.
In case you are still using Python 2 (but please use Python 3), just add

from __future__ import division

to let Python do the right thing (it won't hurt if you do it in Python 3; it just doesn't do anything). With that (or in Python 3 anyway), you can remove numerous other float() casts you have elsewhere in your code, improving readability.

Answer 2

np.invert 需要整数或布尔值，请改用np.linalg.inv方法。