CODEWITHSUNDEEP
pythonpython-3.xnumpynumpy-ndarray
刘宸宇
刘宸宇

Reputation: 38

How to pick up an element randomly in a numpy array?

enter image description hereI am writing script to realize a perceptron learning algorithm. However, I am having trouble picking up an element randomly in a numpy array. And I don't know whether there is a built-in function in numpy to do that.

def error_rate(w1, w2):
    W = error(w1, w2)
    return((W.sum())/W.size)
def error(w1, w2):
    W = w1!= w2
    #print(W)
    return W

#test of the function 'error rate'
a = np.array([0,0,0,0,1])
b = np.array([0,1,0,0,1])
print (error_rate(a, b))
print(np.random.choice(np.nonzero(error(a, b)), 1))

In the code above, I actually want to check whether the number in a is the same with the number with the same index in b. And pick up randomly from the index k which satisfies a[k]!=b[k]. But it doesn't work.

Upvotes: 1

Views: 280

Answers (2)

6502
6502

Reputation: 114599

You can use the more compact

x = np.random.choice(np.where(a != b)[0])

Upvotes: 1

fuglede
fuglede

Reputation: 18221

The issue here is that np.nonzero returns a tuple in which you only need the first element; here,

np.random.choice(np.nonzero(a != b)[0])

would do the job. You can avoid picking that out by using np.flatnonzero instead; that is, the above is equivalent to

np.random.choice(np.flatnonzero(a != b))

Upvotes: 1

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