Python | Merge key value lists

Last Updated : 26 Jul, 2019

Sometimes, while working with lists, we can come forward with a problem in which we need to perform the merge function in which we have the key list and need to create dictionary mapping keys with corresponding value in other list. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using zip() + loop + defaultdict()
The combination of above method can be used to perform this particular task. In this, we use zip function to match the like elements of lists with each other and loop is then used to assign the keys with value from zipped list to add value to a defaultdict.

# Python3 code to demonstrate working of
# Merge key value list
# Using zip() + loop + defaultdict()
from collections import defaultdict
  
# initializing lists
test_list1 = [0, 0, 0, 1, 1, 1, 2, 2]
test_list2 = ['gfg', 'is', 'best', 'Akash', 'Akshat', 'Nikhil', 'apple', 'grapes']
  
# printing original lists
print("The original list1 is : " + str(test_list1))
print("The original list2 is : " + str(test_list2))
  
# Using zip() + loop + defaultdict()
# Merge key value list
res = defaultdict(list)
for i, j in zip(test_list1, test_list2):
   res[i].append(j)
  
# printing result 
print("The merged key value dictionary is : " + str(dict(res)))

Output :

The original list1 is : [0, 0, 0, 1, 1, 1, 2, 2]
The original list2 is : [‘gfg’, ‘is’, ‘best’, ‘Akash’, ‘Akshat’, ‘Nikhil’, ‘apple’, ‘grapes’]
The merged key value dictionary is : {0: [‘gfg’, ‘is’, ‘best’], 1: [‘Akash’, ‘Akshat’, ‘Nikhil’], 2: [‘apple’, ‘grapes’]}

Method #2 : Using itemgetter() + groupby() + zip()
This is yet another way to perform this particular task. In this, we group the keys fetched by itemgetter to the first list with the elements of other list which is linked using the zip function using groupby method.

# Python3 code to demonstrate working of
# Merge key value list
# Using itemgetter() + groupby() + zip()
from itertools import groupby
from operator import itemgetter
  
# initializing lists
test_list1 = [0, 0, 0, 1, 1, 1, 2, 2]
test_list2 = ['gfg', 'is', 'best', 'Akash', 'Akshat', 'Nikhil', 'apple', 'grapes']
  
# printing original lists
print("The original list1 is : " + str(test_list1))
print("The original list2 is : " + str(test_list2))
  
# Using itemgetter() + groupby() + zip()
# Merge key value list
res = {keys: [i for _, i in sub] for keys, sub in groupby(
         zip(test_list1, test_list2), key = itemgetter(0))}
  
# printing result 
print("The merged key value dictionary is : " + str(dict(res)))

Output :

The original list1 is : [0, 0, 0, 1, 1, 1, 2, 2]
The original list2 is : [‘gfg’, ‘is’, ‘best’, ‘Akash’, ‘Akshat’, ‘Nikhil’, ‘apple’, ‘grapes’]
The merged key value dictionary is : {0: [‘gfg’, ‘is’, ‘best’], 1: [‘Akash’, ‘Akshat’, ‘Nikhil’], 2: [‘apple’, ‘grapes’]}

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