Python - 查找所有嵌套列表的起始索引

在本文中给出一个矩阵，任务是编写一个Python程序来计算所有嵌套列表的起始索引。

例子：

Input : test_list = [[5], [9, 3, 1, 4], [3, 2], [4, 7, 8, 3, 1, 2], [3, 4, 5]]

Output : [0, 1, 5, 7, 13]

Explanation : 1 + 4 = lengths of 2 initial lists = 5, 3, of 3rd list start from 5th index [ 0 based indexing ], 

hence 5. as 3rd element in result list.

Input : test_list = [[5], [9, 3, 1, 4], [3, 2], [3, 4, 5]]

Output : [0, 1, 5, 7]

Explanation : 1 + 4 = lengths of 2 initial lists = 5, 3, of 3rd list start from 5th index [ 0 based indexing ],

hence 5. as 3rd element in result list.

方法 #1：使用循环 + len()

在这种情况下，每个子列表的长度使用 len() 计算并求和，累积，并作为中间结果添加。初始索引是子列表长度的导数。

Python3

# Python3 code to demonstrate working of
# Initial element index in Matrix
# Using loop
 
# initializing list
test_list = [[5], [9, 3, 1, 4], [3, 2], [4, 7, 8, 3, 1, 2], [3, 4, 5]]
 
# printing original list
print("The original list is : " + str(test_list))
 
res = []
lens = 0
for sub in test_list:
 
    # lengths of sublist computed
    res.append(lens)
    lens += len(sub)
 
# printing result
print("Initial element indices : " + str(res))

输出：

The original list is : [[5], [9, 3, 1, 4], [3, 2], [4, 7, 8, 3, 1, 2], [3, 4, 5]]

Initial element indices : [0, 1, 5, 7, 13]

方法#2：使用accumulate() + map() + len()

在这里，我们使用accumulate() 执行求和任务，map() 用于获得使用len() 计算的所有子列表的长度。

蟒蛇3

# Python3 code to demonstrate working of
# Initial element index in Matrix
# Using accumulate() + map() + len()
from itertools import accumulate
 
# initializing list
test_list = [[5], [9, 3, 1, 4], [3, 2], [4, 7, 8, 3, 1, 2], [3, 4, 5]]
 
# printing original list
print("The original list is : " + str(test_list))
 
# ignoring last index using "-1"
# sum starting at 0
res = [0, *accumulate(map(len, test_list[:-1]))]
 
# printing result
print("Initial element indices : " + str(res))

输出：

The original list is : [[5], [9, 3, 1, 4], [3, 2], [4, 7, 8, 3, 1, 2], [3, 4, 5]]

Initial element indices : [0, 1, 5, 7, 13]

方法 #3：使用 type() 和循环以及 if 语句

在这里，我们只需检查列表中元素的类型，如果它是另一个列表，我们将打印其索引，否则不会。无论列表中非列表类型元素的数量如何，此方法都将起作用

蟒蛇3

# This will print all the starting indexes
# of sublists inside this list
lis = [[1,2,3],4,5,[6,7,8],9,0,[10]]
 
for i in lis:
    if type(i) == list:
        print(lis.index(i), end=",")
         
# This code is contributed by BABAji

输出：

0,3,6,