Python – Group Similar items to Dictionary Values List

Given a list of elements, perform grouping of similar elements, as different key-value list in dictionary.

Input : test_list = [4, 6, 6, 4, 2, 2, 4, 8, 5, 8]
Output : {4: [4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}
Explanation : Similar items grouped together on occurrences.

Input : test_list = [7, 7, 7, 7]
Output : {7 : [7, 7, 7, 7]}
Explanation : Similar items grouped together on occurrences.

Method #1 : Using defaultdict() + loop

This is one of the ways in which this task can be performed. In this, we construct a defaultdict() with default list and keep appending similar values into similar list.



Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 code to demonstrate working of 
# Group Similar items to Dictionary Values List
# Using defaultdict + loop
from collections import defaultdict
  
# initializing list
test_list = [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
  
# printing original list
print("The original list : " + str(test_list))
  
# using defaultdict for default list 
res = defaultdict(list)
for ele in test_list:
      
    # appending Similar values
    res[ele].append(ele)
  
# printing result 
print("Similar grouped dictionary : " + str(dict(res)))

chevron_right


Output

The original list : [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
Similar grouped dictionary : {4: [4, 4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}

Method #2 : Using dictionary comprehension + Counter()

This is yet another way in which this task can be performed. In this, we extract frequency using Counter() and then repeat occurrences using multiplication.

Python3

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 code to demonstrate working of 
# Group Similar items to Dictionary Values List
# Using dictionary comprehension + Counter()
from collections import Counter
  
# initializing list
test_list = [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
  
# printing original list
print("The original list : " + str(test_list))
  
# using * operator to perform multiplication
res = {key : [key] * val for key, val in Counter(test_list).items()}
  
# printing result 
print("Similar grouped dictionary : " + str(res))

chevron_right


Output

The original list : [4, 6, 6, 4, 2, 2, 4, 4, 8, 5, 8]
Similar grouped dictionary : {4: [4, 4, 4, 4], 6: [6, 6], 2: [2, 2], 8: [8, 8], 5: [5]}

Attention geek! Strengthen your foundations with the Python Programming Foundation Course and learn the basics.

To begin with, your interview preparations Enhance your Data Structures concepts with the Python DS Course.




My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.