vstack() function and hstack() function in array connection

vstack() function and hatack() function

The vstack() function connects two arrays vertically.

The hatack() function concatenates two arrays horizontally.

When the array type is a one-dimensional array

Look at the code below:

import numpy as np

arr1 = np.array([1, 2, 3])
arr2 = np.array([4, 5, 6])
# 竖直方向上连接
print(np.vstack((arr1, arr2)))
#水平方向上连接
print(np.hstack((arr1, arr2)))

The output result is:

[[1 2 3]
 [4 5 6]]
 
[1 2 3 4 5 6]

When the array type is a two-dimensional array

The code shows:

import numpy as np

arr1 = np.array([[1, 2], [3, 4], [5, 6]])
arr2 = np.array([[7, 8], [9, 10], [11,12]])
print(np.vstack((arr1, arr2)))
print(np.hstack((arr1, arr2)))

The output result is:

[[ 1  2]
 [ 3  4]
 [ 5  6]
 [ 7  8]
 [ 9 10]
 [11 12]]
 
[[ 1  2  7  8]
 [ 3  4  9 10]
 [ 5  6 11 12]]

When the sizes of two connected array types are inconsistent

If the code looks like this it will go wrong:
case one

import numpy as np

arr1 = np.array([[1, 2], [3, 4], [5, 6]])
arr2 = np.array([[7, 8], [9, 10], [11]])
print(np.vstack((arr1, arr2)))
print(np.hstack((arr1, arr2)))
# 此种情况输出错误

case two

import numpy as np

arr1 = np.array([[1, 2], [3, 4], [5, 6]])
arr2 = np.array([[7, 8], [9, 10], [11,12，13]])
print(np.vstack((arr1, arr2)))
print(np.hstack((arr1, arr2)))
# 此种情况输出错误

Case three:

import numpy as np

arr1 = np.array([[1, 2], [3, 4], [5, 6]])
arr2 = np.array([[7, 8], [9, 10]])
print(np.vstack((arr1, arr2)))
print(np.hstack((arr1, arr2)))

In this case, there is no problem with the first output, and the correct output result can be obtained. But there is still a problem with the latter output, because there is no principle of ensuring row equality in the subarray.