CODEWITHSUNDEEP
pythonlistdictionary
AMisra
AMisra

Reputation: 1889

Efficiently merge lists into a list of dictionaries

I have 2 lists and I want to merge them as list of dictionaries. The code I have:

import pprint

list1 = [1, 2, 3, 4]
list2 = [0, 1, 1, 2]
newlist = []
for i in range(0, len(list1)):
    newdict = {}
    newdict["original"] = list1[i]
    newdict["updated"] = list2[i]
    newlist.append(newdict)
pprint.pprint(newlist)

Output:

[{'original': 1, 'updated': 0},
 {'original': 2, 'updated': 1},
 {'original': 3, 'updated': 1},
 {'original': 4, 'updated': 2}]

Is there a better or faster way to do this?

Upvotes: 2

Views: 319

Answers (3)

Cyb3rFly3r
Cyb3rFly3r

Reputation: 1341

The answer provided by idjaw nails it in a very Pythonic way. There is an alternative approach using named tuples:

from collections import namedtuple
from itertools import izip
ListCompare = namedtuple('ListCompare', ['original', 'updated'])
L1 = [1,2,3,4]
L2 = [0,1,1,2]
comp = [ListCompare(a, b) for a,b in izip(L1, L2)]
print comp[1].original, comp[1].updated

2 1

Named tuples should perform better (i.e. less overhead) than dictionaries if the lists are long. Just though I'd mention this less known alternative. Note that this code is for Python 2.7, for Python 3 one must make minor adjustments.

Upvotes: 0

idjaw
idjaw

Reputation: 26578

You can zip your two lists and then use a list comprehension, where you create your dictionary as each item in the list: 

list1=[1,2,3,4]
list2=[0,1,1,2]

new_list = [{'original': v1, 'updated': v2} for v1, v2 in zip(list1, list2)]

print(new_list)

Output:

[{'updated': 0, 'original': 1}, {'updated': 1, 'original': 2}, {'updated': 1, 'original': 3}, {'updated': 2, 'original': 4}]

Upvotes: 13

billieD
billieD

Reputation: 1

You could also iterate over both lists at every index with a list comprehension. As is, this will throw an index error if list1 is larger than list2. Anyone know if zip is faster?

newlist = [{"original":list1[i],"updated":list2[i]} for i in range(len(list1))]

Upvotes: 0

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