Python – Frequencies of Values in a Dictionary
Last Updated : 25 Apr, 2023
Sometimes, while working with python dictionaries, we can have a problem in which we need to extract the frequency of values in the dictionary. This is quite a common problem and has applications in many domains including web development and day-day programming. Let’s discuss certain ways in which this task can be performed.
Input : test_dict = {‘ide’ : 3, ‘Gfg’ : 3, ‘code’ : 2}
Output : {3: 2, 2: 1}
Input : test_dict = {10 : 1, 20 : 2, 30 : 1, 40 : 2 }
Output : {1 : 2, 2 : 2}
Method #1 : Using defaultdict() + loop The combination of above functions can be used to solve this problem. In this, we use defaultdict() to initialize the counter dictionary with integers and increment counter in brute force manner using loop.
Python3
from collections import defaultdict
test_dict = {'ide' : 3, 'Gfg' : 3, 'code' : 2}
print("The original dictionary : " + str(test_dict))
res = defaultdict(int)
for key, val in test_dict.items():
res[val] += 1
print("The frequency dictionary : " + str(dict(res)))
|
Output: The original dictionary : {'Gfg': 3, 'code': 2, 'ide': 3} The frequency dictionary : {2: 1, 3: 2} Time Complexity: O(n), where n is the length of the list test_list
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the res list
Method #2 : Using Counter() + values() The combination of above functions can be used to solve this problem. In this, we perform the task of extraction of values using values() and frequency counter using Counter().
Python3
from collections import Counter
test_dict = {'ide' : 3, 'Gfg' : 3, 'code' : 2}
print("The original dictionary : " + str(test_dict))
res = Counter(test_dict.values())
print("The frequency dictionary : " + str(dict(res)))
|
Output: The original dictionary : {'code': 2, 'Gfg': 3, 'ide': 3} The frequency dictionary : {2: 1, 3: 2} Method #3 : Using values(),count(),list(),set() methods
Approach
- Create an empty dictionary res, store the values of dictionary in a list x(list(),values())
- Store the unique values of a list x in list y(using list(),set())
- Initiate a for loop to traverse unique values list y
- Inside for loop with unique value as key and count of unique value in list y as value(using count())
- Display output dictionary res
Python3
test_dict = {'ide' : 3, 'Gfg' : 3, 'code' : 2}
print("The original dictionary : " + str(test_dict))
res=dict()
x=list(test_dict.values())
y=list(set(x))
for i in y:
res[i]=x.count(i)
print("The frequency dictionary : " + str(res))
|
Output The original dictionary : {'ide': 3, 'Gfg': 3, 'code': 2} The frequency dictionary : {2: 1, 3: 2} Time Complexity: O(N), where N is the length of dictionary values list
Auxiliary Space: O(N)
Method #4: Using values(),operator.countOf(),list(),set() methods
Step-by-step approach:
- Create an empty dictionary res, store the values of dictionary in a list x(list(),values())
- Store the unique values of a list x in list y(using list(),set())
- Initiate a for loop to traverse unique values list y
- Inside for loop with unique value as key and count of unique value in list y as value(using operator.countOf())
- Display output dictionary res
Below is the implementation of the above approach:
Python3
test_dict = {'ide' : 3, 'Gfg' : 3, 'code' : 2}
print("The original dictionary : " + str(test_dict))
res=dict()
x=list(test_dict.values())
y=list(set(x))
import operator
for i in y:
res[i]=operator.countOf(x,i)
print("The frequency dictionary : " + str(res))
|
Output The original dictionary : {'ide': 3, 'Gfg': 3, 'code': 2} The frequency dictionary : {2: 1, 3: 2} Time Complexity: O(N), where N is the length of dictionary values list
Auxiliary Space: O(N)
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