numpy 从二维数组中减去/添加一维数组 [英] numpy subtract/add 1d array from 2d array

问题描述

我有以下二维数组:

a = array([[ 1,  2,  3],
           [ 4,  5,  6],
           [ 7,  8,  9],
           [10, 11, 12],
           [13, 14, 15]])

和另一个一维数组:

b = array([ 1,  2,  3,  4,  5])

然后我想计算类似

c = a - b

意图获得:

c = array([[0, 1,  2],
           [2, 3,  4],
           [4, 5,  6],
           [6, 7,  8],
           [8, 9, 10]])

但我收到了错误消息:

Traceback (most recent call last):
  Python Shell, prompt 79, line 1
ValueError: operands could not be broadcast together with shapes (5,3) (5,)

我阅读了广播规则，但并没有变得更明智.我可以用 for-loops 或类似方法做一个解决方法，但应该有一个直接的方法.谢谢

I read the broadcasting rules but didn´t get any wiser. I could do a workaround with for-loops or similar but there should be a direct way. Thanks

推荐答案

需要将数组b转成(2, 1)形数组，使用None或numpy.newaxis 在索引元组中.这是Numpy 数组的索引.

You need to convert array b to a (2, 1) shape array, use None or numpy.newaxis in the index tuple. Here is the Indexing of Numpy array.

你可以这样做:

import numpy

a = numpy.array([[ 1,  2,  3],
           [ 4,  5,  6],
           [ 7,  8,  9],
           [10, 11, 12],
           [13, 14, 15]])

b = numpy.array([ 1,  2,  3,  4,  5])
c=a - b[:,None]
print c

输出:

Out[2]: 
array([[ 0,  1,  2],
       [ 2,  3,  4],
       [ 4,  5,  6],
       [ 6,  7,  8],
       [ 8,  9, 10]])

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