在将numpy数组与其他两个numpy数组组成元素时出现广播错误 [英] Broadcasting error when forming numpy array with elements as two other numpy arrays

问题描述

我正在尝试生成一个具有与其他两个numpy数组相同的元素的numpy数组，如下所示.

I am trying to generate a numpy array with elements as two other numpy arrays, as below.

W1b1 = np.zeros((256, 161))
W2b2 = np.zeros((256, 257))
Wx = np.array([W1b1, W2b2], dtype=np.object)

这给出了一个错误:

ValueError: could not broadcast input array from shape (256,161) into shape (256).

但是，如果我对W1b1和W2b2采取完全不同的尺寸，那么我不会得到错误，如下所示.

However, if I take entirely different dimensions for of W1b1 and W2b2 then I do not get an error, as below.

A1 = np.zeros((256, 161))
A2 = np.zeros((257, 257))
A3 = np.array([A1, A2], dtype=np.object)

我没有理解第一个代码中的错误，为什么numpy数组试图广播一个输入数组.

I do not get what is wrong in the first code and why is numpy array trying to broadcast one of the input arrays.

我尝试使用以下版本(Python 2.7.6，Numpy 1.13.1)和(Python 3.6.4，Numpy 1.14.1).

I have tried on below versions (Python 2.7.6, Numpy 1.13.1) and (Python 3.6.4, Numpy 1.14.1).

推荐答案

不要指望np.array(..., object)建立正确的对象数组.目前，我们无法控制其制作的尺寸.可以想象它可以制作一个(2，)数组或(2，256)(具有1d内容).有时会起作用，有时会引发错误.有某种模式，但是我还没有看到对代码的分析以显示出正在发生的事情.

Don't count on np.array(..., object) making the right object array. At the moment we don't have control over how many dimensions it makes. Conceivably it could make a (2,) array, or (2, 256) (with 1d contents). Sometimes it works, sometimes raises an error. There's something of a pattern, but I haven't seen an analysis of the code that shows exactly what is happening.

现在，分配数组并填充它更安全:

For now it is safer to allocate the array, and fill it:

In [57]: arr = np.empty(2, object)
In [58]: arr[:] = [W1b1, W2b2]

np.array([np.zeros((3,2)),np.ones((3,4))], object)也会引发此错误.因此，当第一个尺寸匹配但第二个尺寸不匹配时，就会出现错误.现在，我开始思考，我之前已经看到过此错误.

np.array([np.zeros((3,2)),np.ones((3,4))], object) also raises this error. So the error arises when the first dimensions match, but the later ones don't. Now that I think about, I've seen this error before.

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