用Numpy数组进行真正除法的问题 [英] Issue with true division with Numpy arrays

问题描述

假设您有以下数组:

In [29]: a = array([[10, 20, 30, 40, 50], [14, 28, 42, 56, 70], [18, 36, 54, 72, 90]])

Out[30]: a
array([[ 0,  0,  0,  0,  0],
       [14, 28, 42, 56, 70],
       [18, 36, 54, 72, 90]])

现在将第三行除以第一行(使用未来导入分区)

Now divide the third row by the first one (using from future import division)

In [32]: a[0]/a[2]
Out[32]: array([ 0.55555556,  0.55555556,  0.55555556,  0.55555556,  0.55555556])

现在对循环中的每一行都执行相同的操作:

Now do the same with each row in a loop:

In [33]: for i in range(3):
            print a[i]/a[2]   
[ 0.55555556  0.55555556  0.55555556  0.55555556  0.55555556]
[ 0.77777778  0.77777778  0.77777778  0.77777778  0.77777778]
[ 1.  1.  1.  1.  1.]

一切看起来都正确.但是现在，将第一个数组a [i]/a [2]分配给a [i]:

Everything looks right. But now, assign the first array a[i]/a[2] to a[i]:

In [35]: for i in range(3):
            a[i]/=a[2]
   ....:     

In [36]: a
Out[36]: 
array([[0, 0, 0, 0, 0],
       [0, 0, 0, 0, 0],
       [1, 1, 1, 1, 1]])

好的，没问题.证明这是设计使然.相反，我们应该这样做:

Alright, no problem. Turns out this is by design. Instead, we should do:

In [38]: for i in range(3):
            a[i] = a[i]/a[2]
   ....:     

In [39]: a
Out[39]: 
array([[0, 0, 0, 0, 0],
       [0, 0, 0, 0, 0],
       [1, 1, 1, 1, 1]])

但这不起作用.为什么以及如何解决?

But that doesn't work. Why and how can I fix it?

提前谢谢.

推荐答案

您可以先将整个数组转换为float数组:

You can cast the whole array to a float array first:

a = a.astype('float')
a /= a[2]

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