将列表转换为 Numpy 二维数组

Question

How to convert a list into a numpy 2D ndarray. For example:

lst = [20, 30, 40, 50, 60]

Expected result:

>> print(arr)
>> array([[20],
       [30],
       [40],
       [50],
       [60]])

>> print(arr.shape)
>> (5, 1)

Answer 1

Convert it to array and reshape:

x = np.array(x).reshape(-1,1)

reshape adds the column structure. The -1 in reshape takes care of the correct number of rows it requires to reshape.

output:

[[20]
 [30]
 [40]
 [50]
 [60]]

Answer 2

If you need your calculations more effective, use numpy arrays instead of list comprehensions. This is an alternative way using array broadcasting

x = [20, 30, 40, 50, 60]
x = np.array(x) #convert your list to numpy array
result = x[:, None] #use numpy broadcasting

if you still need a list type at the end, you can convert your result efficiently using result.tolist()

Answer 3

You may use a list comprehension and then convert it to numpy array:

import numpy as np

x = [20, 30, 40, 50, 60]

x_nested = [[item] for item in x]

x_numpy = np.array(x_nested)