如何将新列添加到现有的csv文件

Question

For instance, x is my data and r is supposed to be new data to be added.

import numpy as np
x = np.array([[1, 2, 3], 
              [4, 5, 6],
              [7, 8, 9]], np.int32)
np.savetxt("test.csv", x, fmt='%d', delimiter=',')

r = [1,2,3]

how could I add it to that "test.csv"

Answer 1

您可以使用numpy中的insert函数插入新列，如下所示

np.insert(x, 3, [r], axis=1)

Answer 2

Isn't this just about adding a column to an existing 2d array. Writing it to a csv file is just a further step and isn't affected by this addition.

In [96]: x = np.array([[1, 2, 3], 
    ...:               [4, 5, 6],
    ...:               [7, 8, 9]], np.int32)
In [97]: r = [1,2,3]

There are a number of functions that can add a column to an array, but they all end up using concatenate . And knowing how to use concatenate directly is a good thing to know. The key is matching the number of dimensions.

In [98]: x1 = np.concatenate((x, np.array(r)[:,None]), axis=1)
In [99]: x1
Out[99]: 
array([[1, 2, 3, 1],
       [4, 5, 6, 2],
       [7, 8, 9, 3]])

vstack takes care of turning r into this column array. insert is more general, allowing you to add values within the existing (not just at the end). But like concatenate (and all the stacks) it does not operate in-place.