CODEWITHSUNDEEP
pythonlist-comprehension
user3206440
user3206440

Reputation: 5049

python list of dicts - extract key-val of lists

With a list of dicts like below

a = [{'a': 1, 'b': [{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}]}, {'a': 2, 'b': [{'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]}]

need to extract values for the key b into another list

I could do the following

b = []
for item in a:
  b+= item['b']

this gives [{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}, {'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}] which is fine.

I'm trying to learn list comprehension and wanted to know how this could be done. I tried the following [ item['b'] for item in a]. However that give a list of lists like below.

[[{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}], [{'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]]

Upvotes: 1

Views: 62

Answers (2)

anbocode
anbocode

Reputation: 73

You can try the following solutions. Solution at number (2) uses Python "itertools" module.

(1)

a = [{'a': 1, 'b': [{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}]}, {'a': 2, 'b': [{'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]}]

[ r for item in a for r in item['b']]

Output...

[{'c': [1, 2, 3], 'd': 4},
 {'c': [5, 6, 1], 'd': 7},
 {'c': [2, 3, 4], 'd': 5},
 {'c': [7, 6, 1], 'd': 8}]

(2)

a = [{'a': 1, 'b': [{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}]}, {'a': 2, 'b': [{'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]}]

import itertools
list(itertools.chain.from_iterable([item['b'] for item in a]))

Output...

[{'c': [1, 2, 3], 'd': 4},
 {'c': [5, 6, 1], 'd': 7},
 {'c': [2, 3, 4], 'd': 5},
 {'c': [7, 6, 1], 'd': 8}]

Upvotes: 1

Bernardo stearns reisen
Bernardo stearns reisen

Reputation: 2657

I would try something like this, just keep in mind the outer loop would come first than the inner loop in the list comprehension

a = [{'a': 1, 'b': [{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}]}, {'a': 2, 'b': [{'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]}]

b = [ c for d in a for c in d['b']]
print(b)

OUTPUTS:

[{'c': [1, 2, 3], 'd': 4}, {'c': [5, 6, 1], 'd': 7}, {'c': [2, 3, 4], 'd': 5}, {'c': [7, 6, 1], 'd': 8}]

Upvotes: 5

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