将项目添加到列表中的特定位置

Question

x=len(sorted_list)
z=1
for y in range (2,x):
    if sorted_list[y][1]=="0" and len(sorted_list[y])>3:
        z+=1
        sorted_list.insert(y,'Message '+ str(z))
        x+=1
    else:
        continue

I have a list named "sorted_list". I want to add some items to list but i have a problem. When i try this code it goes to infinity. I want to group numbers by 0th index. I have an input like that:

[['65', '0', 'Hello'],
['65', '1', 'world'],
['78', '0', "what's"],
['78', '1', 'up']]

I want the output like that:

Message 1
65 0 Hello 
65 1 world
Message 2
78 0 what's
78 1 up

Answer 1

In general it's not a great idea to try to modify a list as you're iterating over it, because it's very easy to confuse yourself. Since you just want to print the list contents with extra messages interspersed, I think it's better to just not modify the list and print the messages as you iterate.

The easy way to group things according to specific criteria (in this case the 0th index of each list) is to use itertools.groupby :

>>> from itertools import groupby
>>> for i, (_, group) in enumerate(groupby(sorted_list, lambda i: i[0])):
...     print(f"Message {i+1}")
...     for line in group:
...         print(" ".join(line))
...
Message 1
65 1 Hello
65 2 world
Message 2
78 2 what's
78 3 up

Answer 2

Also you can do it using pandas :

import pandas as pd

sorted_list = [['65', '0', 'Hello'],
['65', '1', 'world'],
['78', '0', "what's"],
['78', '1', 'up']]

df = pd.DataFrame(sorted_list)
groups = df.groupby(0) #group by first column

for i,(name, group) in enumerate(groups):
  print('Message {0}'.format(i+1))
  for c1, c2, c3 in group.to_numpy():
    print(c1,c2,c3)