How to convert list of dict into two lists?

user_3943868 0
Viewed 331

For example:

persons = [{'id': 1, 'name': 'john'}, {'id': 2, 'name': 'mary'}, {'id': 3, 'name': 'tom'}]

I want to get two lists from it:

ids = [1, 2, 3]
names = ['john', 'mary', 'tom']

What I did:

names = [d['name'] for d in persons]
ids = [d['id'] for d in persons]

Is there a better way to do it?

python
5 Answers

What you did works fine. Another way to handle this (not necessarily better, depending on your needs) is to store your data in a more efficient dictionary and pull the names/ids out of it when you need them:

>>> persons = [{'id': 1, 'name': 'john'}, {'id': 2, 'name': 'mary'}, {'id': 3, 'name': 'tom'}]
>>> p2 = {x['id']: x['name'] for x in persons}
>>> p2
{1: 'john', 2: 'mary', 3: 'tom'}

>>> list(p2.keys())
[1, 2, 3]

>>> list(p2.values())
['john', 'mary', 'tom']
user_84518140

I'd stick with using list comprehension or use @Woodford technique

ids,name = [dcts['id'] for dcts in persons],[dcts['name'] for dcts in persons]

output

[1, 2, 3] 
['john', 'mary', 'tom']
user_142222510

You can do it with pandas in a vectorized fashion:

import pandas as pd
persons = [{'id': 1, 'name': 'john'}, {'id': 2, 'name': 'mary'}, {'id': 3, 'name': 'tom'}]

df = pd.DataFrame(persons)
id_list = df.id.tolist() #[1, 2, 3]
name_list = df.name.tolist() #['john', 'mary', 'tom']
user_91620000

It sounds like you're trying to iterate through the values of your list while unpacking your dictionaries:

persons = [{'id': 1, 'name': 'john'}, {'id': 2, 'name': 'mary'}, {'id': 3, 'name': 'tom'}]


for x in persons:
    id, name = x.values()
    ids.append(id)
    names.append(name)
user_105219590

An alternative, inspired by this question, is

ids, names = zip(*map(lambda x: x.values(), persons))

that return tuples. If you need lists

ids, names = map(list, zip(*map(lambda x: x.values(), persons)))

It is a little bit slower on my laptop using python3.9 than the accepted answer but it might be useful.

user_82270620
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