Turning a list of dictionaries into a single larger dictionary

Janet 0
Viewed 46

Maybe this is a simple question, but I've been scratching my head on it.

How do I turn a list of several dictionaries into a single dictionary containing all values?

This is what I mean:

input_list = [
    {'fruit': 'banana',
     'color1': ''},
    {'vegetable': 'tomato',
     'color2': ''},
    {'dessert': 'ice cream',
     'taste': ''}
]

desired_output = {
    'fruit': 'banana',
    'color1': '',
    'vegetable': 'tomato',
    'color2': '',
    'dessert': 'ice cream',
    'taste': ''
}

Any help would be appreciated, thank you in advance.

python
3 Answers

Use this:

output = {key:value for element in input_list for key, value in element.items()}

Output:

{'fruit': 'banana',
 'color1': '',
 'vegetable': 'tomato',
 'color2': '',
 'dessert': 'ice cream',
 'taste': ''}
Shahab Rahnama0

You could just loop through the list and use update() method to merge the dictionaries that is all needed to do:

desired_output = {}
for d in input_list:
  desired_output.update(d)
kavigun0

Introduction

You can merge dict with the | bitwise operator from version 3.9. chaining them, with functools.reduce with operator.or_:

Rough explanation of functools.reduce

 functools.reduce(function, iterable[, initializer])

Apply function of two arguments cumulatively to the items of iterable, from left to right, so as to reduce the iterable to a single value

Here are some examples for functools.reduce:

>>> #calculates ((((1+2)+3)+4)+5) which is the sum
>>> reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) 
15
>>> # factorial of 5 using reduce
>>> n = 4
>>> reduce(lambda x, y: x*y, range(1,n+1))
24

Answer

Using functools.reduce and operator._or here is the code that I come up with:

import operator
from functools import reduce
result = reduce(operator.or_,list_of_dicts)
pprint.pprint(result)

EDIT: As @KellyBundy commented, my implementation is O(n^2) but using operator.ior and the Optional initializer parameter, we could make it linear.

Implementation:

import operator
from functools import reduce
result = reduce(operator.ior,list_of_dicts,{})
pprint(result)

Output

{'fruit': 'banana',
 'color1': '',
 'vegetable': 'tomato',
 'color2': '',
 'dessert': 'ice cream',
 'taste': ''}
XxJames07-0
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