Python | Convert list of tuples to dictionary value lists

Last Updated : 26 Jul, 2019

One among the problem of interconversion of data types in python is conversion of list of tuples to dictionaries, in which the keys are 1st element of tuple, which are uniquely identified as keys in dictionary and it’s corresponding value as list of corresponding value of respective keys as tuple’s second element. Let’s discuss how to solve this particular problem.

Method #1 : Using defaultdict() + loop
This problem can easily be solved using the defaultdict() and loop. The defaultdict provides a default value dictionary container to assign corresponding value list to keys, so that we don’t need to initialize keys with empty list and loop is used to extract like values from tuple.

# Python3 code to demonstrate working of
# Convert list of tuples to dictionary value lists
# Using defaultdict() + loop
from collections import defaultdict
  
# initializing list
test_list = [(1, 'gfg'), (1, 'is'), (2, 'best'), (3, 'for'), (4, 'CS')]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Using defaultdict() + loop
# Convert list of tuples to dictionary value lists
res = defaultdict(list)
for i, j in test_list:
    res[i].append(j)
  
# printing result 
print("The merged dictionary is : " + str(dict(res)))

Output :

The original list is : [(1, ‘gfg’), (1, ‘is’), (2, ‘best’), (3, ‘for’), (4, ‘CS’)]
The merged dictionary is : {1: [‘gfg’, ‘is’], 2: [‘best’], 3: [‘for’], 4: [‘CS’]}

Method #2 : Using defaultdict() + groupby()
This method performs the task similar to above method, just instead of using loop to access each key value pair, here we use Python’s groupby library to group keys with value and convert then into a list.

# Python3 code to demonstrate working of
# Convert list of tuples to dictionary value lists
# Using defaultdict() + groupby()
from collections import defaultdict
from operator import itemgetter
from itertools import groupby
  
# initializing list
test_list = [(1, 'gfg'), (1, 'is'), (2, 'best'), (3, 'for'), (4, 'CS')]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Using defaultdict() + groupby()
# Convert list of tuples to dictionary value lists
res = dict((k, [v[1] for v in itr]) for k, itr in groupby(
                                test_list, itemgetter(0)))
  
# printing result 
print("The merged dictionary is : " + str(dict(res)))

Output :

The original list is : [(1, ‘gfg’), (1, ‘is’), (2, ‘best’), (3, ‘for’), (4, ‘CS’)]
The merged dictionary is : {1: [‘gfg’, ‘is’], 2: [‘best’], 3: [‘for’], 4: [‘CS’]}

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