python-增加数组大小并将新元素初始化为零 [英] python - increase array size and initialize new elements to zero

问题描述

我有一个大小为2 x 2的数组，我想将大小更改为3 x4.

I have an array of a size 2 x 2 and I want to change the size to 3 x 4.

A = [[1 2 ],[2 3]]
A_new = [[1 2 0 0],[2 3 0 0],[0 0 0 0]]

我尝试了3个形状，但没有，附加只能附加行，不能附加列.我不想遍历每一行来添加列.

I tried 3 shape but it didn't and append can only append row, not column. I don't want to iterate through each row to add the column.

是否有任何矢量化方法可以像在MATLAB中那样:A(:,3:4) = 0;和A(3,:) = 0;将A从2 x 2转换为3 x4.我在想是否有类似的方法在python中?

Is there any vectorized way to do this like that of in MATLAB: A(:,3:4) = 0; and A(3,:) = 0; this converted the A from 2 x 2 to 3 x 4. I was thinking is there a similar way in python?

推荐答案

在Python中，如果输入是numpy数组，则可以使用

In Python, if the input is a numpy array, you can use np.lib.pad to pad zeros around it -

import numpy as np

A = np.array([[1, 2 ],[2, 3]])   # Input
A_new = np.lib.pad(A, ((0,1),(0,2)), 'constant', constant_values=(0)) # Output

样品运行-

In [7]: A  # Input: A numpy array
Out[7]: 
array([[1, 2],
       [2, 3]])

In [8]: np.lib.pad(A, ((0,1),(0,2)), 'constant', constant_values=(0))
Out[8]: 
array([[1, 2, 0, 0],
       [2, 3, 0, 0],
       [0, 0, 0, 0]])  # Zero padded numpy array

如果您不想对要填充多少个零的 进行运算，则可以在给定输出数组大小的情况下让代码为您完成-

If you don't want to do the math of how many zeros to pad, you can let the code do it for you given the output array size -

In [29]: A
Out[29]: 
array([[1, 2],
       [2, 3]])

In [30]: new_shape = (3,4)

In [31]: shape_diff = np.array(new_shape) - np.array(A.shape)

In [32]: np.lib.pad(A, ((0,shape_diff[0]),(0,shape_diff[1])), 
                              'constant', constant_values=(0))
Out[32]: 
array([[1, 2, 0, 0],
       [2, 3, 0, 0],
       [0, 0, 0, 0]])

或者，您可以从零初始化输出数组开始，然后从A-

Or, you can start off with a zero initialized output array and then put back those input elements from A -

In [38]: A
Out[38]: 
array([[1, 2],
       [2, 3]])

In [39]: A_new = np.zeros(new_shape,dtype = A.dtype)

In [40]: A_new[0:A.shape[0],0:A.shape[1]] = A

In [41]: A_new
Out[41]: 
array([[1, 2, 0, 0],
       [2, 3, 0, 0],
       [0, 0, 0, 0]])

---

在MATLAB中，您可以使用 padarray -

---

In MATLAB, you can use padarray -

A_new  = padarray(A,[1 2],'post')

样品运行-

>> A
A =
     1     2
     2     3
>> A_new = padarray(A,[1 2],'post')
A_new =
     1     2     0     0
     2     3     0     0
     0     0     0     0

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