如何在 Python 中垂直连接两个数组？
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How to vertically concatenate two arrays in Python?
提问by Eghbal
I want to concatenate two arrays vertically in Python using the NumPy package:
我想使用 NumPy 包在 Python 中垂直连接两个数组：
a = array([1,2,3,4])
b = array([5,6,7,8])
I want something like this:
我想要这样的东西：
c = array([[1,2,3,4],[5,6,7,8]])
How we can do that using the concatenatefunction? I checked these two functions but the results are the same:
我们如何使用该concatenate函数来做到这一点？我检查了这两个函数，但结果是一样的：
c = concatenate((a,b),axis=0)
# or
c = concatenate((a,b),axis=1)
We have this in both of these functions:
我们在这两个函数中都有这个：
c = array([1,2,3,4,5,6,7,8])
采纳答案by Alex Riley
The problem is that both aand bare 1D arrays and so there's only one axis to join them on.
问题是a和b都是一维数组，因此只有一个轴可以连接它们。
Instead, you can use vstack(vfor vertical):
相反，您可以使用vstack（v表示垂直）：
>>> np.vstack((a,b))
array([[1, 2, 3, 4],
[5, 6, 7, 8]])
Also, row_stackis an alias of the vstackfunction:
此外，row_stack是vstack函数的别名：
>>> np.row_stack((a,b))
array([[1, 2, 3, 4],
[5, 6, 7, 8]])
It's also worth noting that multiple arrays of the same length can be stacked at once. For instance, np.vstack((a,b,x,y))would have four rows.
还值得注意的是，可以一次堆叠多个相同长度的数组。例如，np.vstack((a,b,x,y))将有四行。
Under the hood, vstackworks by making sure that each array has at least two dimensions (using atleast_2D) and then calling concatenateto join these arrays on the first axis (axis=0).
在幕后，vstack通过确保每个数组至少有两个维度（使用atleast_2D）然后调用concatenate以在第一个轴 ( axis=0)上连接这些数组来工作。
回答by Ying Xiong
To use concatenate, you need to make aand b2D arrays instead of 1D, as in
要使用concatenate，您需要a和b二维数组，而不是一维，如
c = concatenate((atleast_2d(a), atleast_2d(b)))
Alternatively, you can simply do
或者，你可以简单地做
c = array((a,b))
回答by EdChum
Use np.vstack:
使用np.vstack：
In [4]:
import numpy as np
a = np.array([1,2,3,4])
b = np.array([5,6,7,8])
c = np.vstack((a,b))
c
Out[4]:
array([[1, 2, 3, 4],
[5, 6, 7, 8]])
In [5]:
d = np.array ([[1,2,3,4],[5,6,7,8]])
d
?
Out[5]:
array([[1, 2, 3, 4],
[5, 6, 7, 8]])
In [6]:
np.equal(c,d)
Out[6]:
array([[ True, True, True, True],
[ True, True, True, True]], dtype=bool)
回答by EdChum
Maybe it's not a good solution, but it's simple way to makes your code works, just add reshape:
也许这不是一个好的解决方案，但它是使您的代码正常工作的简单方法，只需添加 reshape：
a = array([1,2,3,4])
b = array([5,6,7,8])
c = concatenate((a,b),axis=0).reshape((2,4))
print c
out:
出去：
[[1 2 3 4]
[5 6 7 8]]
In general if you have more than 2 arrays with the same length:
通常，如果您有 2 个以上相同长度的数组：
reshape((number_of_arrays, length_of_array))
