numpy:逐行减去2个numpy数组 [英] Numpy: Subtract 2 numpy arrays row wise

问题描述

我有2个numpy数组a和b，如下所示:

I have 2 numpy arrays a and b as below:

a = np.random.randint(0,10,(3,2))
Out[124]: 
array([[0, 2],
       [6, 8],
       [0, 4]])
b = np.random.randint(0,10,(2,2))
Out[125]: 
array([[5, 9],
       [2, 4]])

我想从a的每一行中减去b中的每一行，并且所需的输出为shape(3,2,2):

I want to subtract each row in b from each row in a and the desired output is of shape(3,2,2):

array([[[-5, -7],        [-2, -2]],

       [[ 1, -1],        [ 4,  4]],

       [[-5, -5],        [-2,  0]]])

我可以使用:

print(np.c_[(a - b[0]),(a - b[1])].reshape(3,2,2))

但是我需要一个完全矢量化的解决方案或一个内置的numpy函数来做到这一点.

But I need a fully vectorized solution or a built in numpy function to do this.

推荐答案

只需使用np.newaxis(这只是None的别名)即可向a添加单例维度，然后由广播来完成其余工作:

Just use np.newaxis (which is just an alias for None) to add a singleton dimension to a, and let broadcasting do the rest:

In [45]: a[:, np.newaxis] - b
Out[45]: 
array([[[-5, -7],
        [-2, -2]],

       [[ 1, -1],
        [ 4,  4]],

       [[-5, -5],
        [-2,  0]]])

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