从一个包含列表的列表中制作一个关于 python 的字典

Question

i have created a list that has lists in it;

[['2020/10/07', 'AA123', '19.24', '22.00'],
 ['2020/11/17', 'BBB123', '23.59', '00.00'],
 ['2020/14/67', 'AAA123', '08.00', '16.00']]

Problem 1: However I'm unsure on how to turn this list into a dictionary. I've tried several times and nothing works for me. I want the second value in each list(index 1) to be the key for the dictionary and the rest to be values.

Problem 2: If the second element in each list exists in more than one list, I want them to be found under the same key.

Answer 1

Try this:

my_dict = {}
for sub_list in vals:
    val_key = sub_list[1]
    if val_key in my_dict:
        my_dict[val_key].extend([sub_list[0]] + sub_list[2:])
    else:
        my_dict[val_key] = [sub_list[0]] + sub_list[2:]

1. Create an empty dictionary to place your values into.
2. Go through all entries in your data.
3. Key the key for that entry ( sub_list[1] ), we'll use this to index our dictionary.
4. If that key already exists, extend the value stored at that list with this item's non [1] values (eg ['a', 'b', 'c'] becomes ['a', 'b', 'c', 'd', 'e'] for example).
5. If that key doesn't exist, just create a new key in the dictionary with the non [1] values.

Answer 2

You can first extract the keys and values from you first list using list comprehension:

keys = [row[1] for row in l]
values = [[row[0], row[2],row[3]] for row in l]

And then create the dictionnary using the same technique:

{k:v for k,v in zip(keys,values)}

(the zip function allows to iterate over the 2 lists keys and values simultaneously)

For Problem 2: unfortunately you can't have the same key multiple times in a dictionnary, you may have to use len(keys) == len(set(keys)) to test if your keys list have duplicates (the set function extracts all unique values from the list).

Answer 3

raw = [
#     <date>      <key>     <val1>   <val2>
  ['2020/10/07', 'AAA123', '19.24', '22.00'],
  ['2020/11/17', 'BBB123', '23.59', '00.00'],
  ['2020/14/67', 'AAA123', '08.00', '16.00'],
]

(edited your example slightly to have a duplicate key)

It sounds like you want your output to be something like this:

{key: [info, ...], ...}

we can do this as follows:

from collections import defaultdict, namedtuple
Data = namedtuple('Data', ('date', 'val1', 'val2'))
res = defaultdict(list)
for date, key, val1, val2 in raw:
    data = Data(date, val1, val2)
    res[key].append(data)
res = dict(res)  # Strip defaultdict behavior

then we can see

import pprint
pprint.pprint(res)

gives us a result similar to that desired:

{'AAA123': [Data(date='2020/10/07', val1='19.24', val2='22.00'),
            Data(date='2020/14/67', val1='08.00', val2='16.00')],
 'BBB123': [Data(date='2020/11/17', val1='23.59', val2='00.00')]}