RuntimeWarning:除以零错误:如何避免? PYTHON，NUMPY [英] RuntimeWarning: Divide by Zero error: How to avoid? PYTHON, NUMPY

问题描述

我正在运行RuntimeWarning:除法中遇到无效的值

I am running in to RuntimeWarning: Invalid value encountered in divide

 import numpy
 a = numpy.random.rand((1000000, 100))
 b = numpy.random.rand((1,100))
 dots = numpy.dot(b,a.T)/numpy.dot(b,b)
 norms = numpy.linalg.norm(a, axis =1)
 angles = dots/norms ### Basically I am calculating angle between 2 vectors 

我的a中有一些向量的范数为0.因此在计算角度时会发出运行时警告.

There are some vectors in my a which have norm as 0. so while calculating angles it is giving runtime warning.

在考虑0范数的情况下，是否存在一种单线pythonic方法来计算角度?

Is there a one line pythonic way to compute angles while taking into account norms which are 0?

angles =[i/j if j!=0 else -2 for i,j in zip(dots, norms)] # takes 10.6 seconds

但是要花很多时间.由于所有角度的值都在1到-1之间，我只需要10个最大值就可以了.这大约需要10.6秒，这太疯狂了.

But it takes a lot of time. Since all angles will have values between 1 and -1 and I need only 10 max values this will help me. This takes around 10.6 seconds which is insane.

推荐答案

您可以使用np.errstate上下文管理器忽略警告，然后将nans替换为您想要的内容:

you can ignore warings with the np.errstate context manager and later replace nans with what you want:

import numpy as np
angle = np.arange(-5., 5.) 
norm = np.arange(10.)
with np.errstate(divide='ignore'):
    print np.where(norm != 0., angle / norm, -2)
# or:
with np.errstate(divide='ignore'):
    res = angle/norm
res[np.isnan(res)] = -2

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