在python中附加到二维数组

Question

我正在阅读来自CSV文件的数据，该文件类似于以下矩阵/数组

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

我想将大于1的每个元素的索引更改为arraylist中的新行

这将使上面的数组如下

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

我在python中做了什么（但无法得到答案）

b = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
c = b
rows = len(b)
columns = len(b[0])
c[4].append(1)
count = 3
for i in  range(rows):
 for j in  range(columns):
     if i > 1:
         for k in columns
             list1 = 
             c.insert(count,list1)
             count = count + 1

Answer 1

您可以使用numpy。最后执行indexing和concatenate：

import numpy as np
b = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]])
print(np.concatenate((b[:,:2], b[:,2:])))

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

Answer 2

使用列表理解。

<强>实施例

b = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]
n = 2
b = [j[i:i+n] for j in b for i in range(0, len(j), n)]
b = b[0::2] + b[1::2]
print(b)

<强>输出：

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

Answer 3

为什么不将它分成两个列表，然后重新组合它们？

new_elements = []
for i in range(len(b)):
    if len(b[i]) > 2:
        new_elements.append(b[i][2:])
    b[i] = b[i][:2]
b.extend(new_elements)

Answer 4

您可能希望使用numpy数组和concatenate函数。

import numpy as np
b = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]) # or b = np.array(b)
c = np.concatenate((b[:, :2], b[:, 2:]),0)

如果您更喜欢使用python数组，可以使用列表解释：

c = [row[:2] for row in b]
c.extend([row[2:] for row in b])

返回

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

Answer 5

另一种方法是：

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

step = 2
length = len(b[0])
b = [elem[i:i+step] for i in range(0,length,step) for elem in b]
print(b)

输出：

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

Answer 6

data =[]
data.append(['a',1])
data.append(['b',2])
data.append(['c',3])
data.append(['d',4])
print(data)

输出

[[''a'，1]，['b'，2]，['c'，3]，['d'，4]]

Answer 7

单行解决方案np.array(b).reshape(-1,2)：

import numpy as np
b = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]]

np.array(b).reshape(-1,2)

array([[ 1,  2],
       [ 3,  4],
       [ 5,  6],
       [ 7,  8],
       [ 9, 10],
       [11, 12]])