Python|在 numpy 数组中添加行/列的方法

给定 numpy 数组，任务是根据要求向 numpy 数组添加行/列。让我们看几个这个问题的例子。
方法 #1：使用 np.hstack() 方法

Python3

# Python code to demonstrate
# adding columns in numpy array
 
import numpy as np
 
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
 
# printing initial array
print("initial_array : ", str(ini_array));
 
# Array to be added as column
column_to_be_added = np.array([1, 2, 3])
 
# Adding column to numpy array
result = np.hstack((ini_array, np.atleast_2d(column_to_be_added).T))
 
# printing result
print ("resultant array", str(result))

输出：

initial_array :  [[ 1  2  3]
 [45  4  7]
 [ 9  6 10]]
resultant array [[ 1  2  3  1]
 [45  4  7  2]
 [ 9  6 10  3]]

方法 #2：使用 column_stack() 方法

Python3

# python code to demonstrate
# adding columns in numpy array
 
import numpy as np
 
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
 
# printing initial array
print("initial_array : ", str(ini_array));
 
# Array to be added as column
column_to_be_added = np.array([1, 2, 3])
 
# Adding column to numpy array
result = np.column_stack((ini_array, column_to_be_added))
 
# printing result
print ("resultant array", str(result))

输出：

initial_array :  [[ 1  2  3]
 [45  4  7]
 [ 9  6 10]]
resultant array [[ 1  2  3  1]
 [45  4  7  2]
 [ 9  6 10  3]]

方法#3：使用 np.vstack() 方法

Python3

# python code to demonstrate
# adding rows in numpy array
 
import numpy as np
 
ini_array = np.array([[1, 2, 3], [45, 4, 7], [9, 6, 10]])
 
# printing initial array
print("initial_array : ", str(ini_array));
 
# Array to be added as row
row_to_be_added = np.array([1, 2, 3])
 
# Adding row to numpy array
result = np.vstack ((ini_array, row_to_be_added) )
 
# printing result
print ("resultant array", str(result))

输出：

initial_array :  [[ 1  2  3]
 [45  4  7]
 [ 9  6 10]]
resultant array [[ 1  2  3]
 [45  4  7]
 [ 9  6 10]
 [ 1  2  3]]

有时我们有一个空数组，我们需要在其中追加行。 Numpy 提供了使用numpy.append()函数将行追加到空 Numpy 数组的函数。

Syntax : numpy.append(arr, values, axis=None)

案例 1 ：向空的二维数组添加新行

Python3

# importing Numpy package
import numpy as np  
 
# creating an empty 2d array of int type
empt_array = np.empty((0,2), int)
print("Empty array:")
print(empt_array)
 
# adding two new rows to empt_array
# using np.append()
empt_array = np.append(empt_array, np.array([[10,20]]), axis=0)
empt_array = np.append(empt_array, np.array([[40,50]]), axis=0)
 
print("\nNow array is:")
print(empt_array)

Empty array:
[]

Now array is:
[[10 20]
[40 50]]

案例 2 ：向空的 3-D 数组添加新行

Python3

# importing Numpy package
import numpy as np  
 
# creating an empty 3d array of int type
empt_array = np.empty((0,3), int)
print("Empty array:")
print(empt_array)
 
# adding three new rows to empt_array
# using np.append()
empt_array = np.append(empt_array, np.array([[10,20,40]]), axis=0)
empt_array = np.append(empt_array, np.array([[40,50,55]]), axis=0)
empt_array = np.append(empt_array, np.array([[40,50,55]]), axis=0)
 
print("\nNow array is:")
print(empt_array)

Empty array:
[]

Now array is:
[[10 20 40]
 [40 50 55]
 [40 50 55]]

案例 3 ：向空的 4-D 数组添加新行

Python3

# importing Numpy package
import numpy as np  
 
# creating an empty 4d array of int type
empt_array = np.empty((0,4), int)
print("Empty array:")
print(empt_array)
 
# adding four new rows to empt_array
# using np.append()
empt_array = np.append(empt_array, np.array([[100,200,400,888]]), axis=0)
empt_array = np.append(empt_array, np.array([[405,500,550,558]]), axis=0)
empt_array = np.append(empt_array, np.array([[404,505,555,145]]), axis=0)
empt_array = np.append(empt_array, np.array([[44,55,550,150]]), axis=0)
 
print("\nNow array is:")
print(empt_array)

Empty array:
[]

Now array is:
[[100 200 400 888]
 [405 500 550 558]
 [404 505 555 145]
 [ 44  55 550 150]]