Python - Flatten the list of dictionaries

Question

List of dictionaries:

data = [{
         \'a\':{\'l\':\'Apple\',
                \'b\':\'Milk\',
                \'d\':\'Meatball\'},
         \'b\':{\'favou         


        

Answer 1

You can do the following, using itertools.chain:

>>> from itertools import chain
# timeit: ~3.40
>>> [dict(chain(*map(dict.items, d.values()))) for d in data]
[{'l': 'Apple', 
  'b': 'Milk', 
  'd': 'Meatball', 
  'favourite': 'coke', 
  'dislike': 'juice'}, 
 {'l': 'Apple1', 
  'b': 'Milk1', 
  'dislike': 'juice3', 
  'favourite': 'coke2', 
  'd': 'Meatball2'}]

The usage of chain, map, * make this expression a shorthand for the following doubly nested comprehension which actually performs better on my system (Python 3.5.2) and isn't that much longer:

# timeit: ~2.04
[{k: v for x in d.values() for k, v in x.items()} for d in data]
# Or, not using items, but lookup by key
# timeit: ~1.67
[{k: x[k] for x in d.values() for k in x} for d in data]

Note:

RoadRunner's loop-and-update approach outperforms both these one-liners at timeit: ~1.37