Python Dict Comprehension to Create and Update Dictionary

Question

I have a list of dictionaries (data) and want to convert it into dictionary (x) as below. I am using following ‘for loop’ to achieve.

data = [{'Dept': '0123', 'Name': 'Tom'},
        {'Dept': '0123', 'Name': 'Cheryl'},
        {'Dept': '0123', 'Name': 'Raj'},
        {'Dept': '0999', 'Name': 'Tina'}]
x = {}

for i in data:
    if i['Dept'] in x:
        x[i['Dept']].append(i['Name'])
    else:
        x[i['Dept']] = [i['Name']]

Output:
x -> {'0999': ['Tina'], '0123': ['Tom', 'Cheryl', 'Raj']}

Is it possible to implement the above logic in dict comprehension or any other more pythonic way?

score 11 · Accepted Answer · edited Jan 25 '23 at 13:35

11

The dict comprehension, even though not impossible, might not be the best choice. May I suggest using a defaultdict:

from collections import defaultdict

dic = defaultdict(list)
for i in data:
    dic[i['Dept']].append(i['Name'])

edited Jan 25 '23 at 13:35

Tomerikoo

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answered Apr 16 '15 at 16:08

Julien Spronck

15,069
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score 5 · Answer 2 · answered Apr 16 '15 at 16:06

5

It seems way too complicated to be allowed into any code that matters even the least bit, but just for fun, here you go:

{
    dept: [item['Name'] for item in data if item['Dept'] == dept]
    for dept in {item['Dept'] for item in data}
}

answered Apr 16 '15 at 16:06

Underyx

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2

I don't consider it too complicated at all. However, it's slower in a big-O sense, because the data has to be re-scanned once for each unique key found - worst-case O(N^2). – Karl Knechtel Apr 16 '15 at 16:08

Python Dict Comprehension to Create and Update Dictionary

2 Answers2

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