Python – Values frequencies of key

Last Updated : 04 May, 2020

Sometimes, while working with Python dictionary lists, one can have a problem in which we require to find the frequency of all the values occurring in a specific key in dictionary list. This can have application across many domains including web development. Let’s discuss certain ways in which this task can be performed.

Input : test_list = [{‘gfg’: [1]}, {‘good’: [5, 78, 10], ‘gfg’: [5, 6, 7, 8]}]
Output : {8: 1, 1: 1, 5: 1, 6: 1, 7: 1}
Input : test_list = [{‘gfg’: [1, 5, 6, 7]}]
Output : {1: 1, 5: 1, 6: 1, 7: 1}

Method #1 : Using Counter() + list comprehension
The combination of above functionalities is used to solve this problem. In this, we perform the task of finding frequency using Counter() and computation is done using list comprehension.

# Python3 code to demonstrate working of 
# Values frequencies of key
# Using Counter() + list comprehension
from collections import Counter
  
# initializing list
test_list = [{'gfg' : [1, 5, 6, 7], 'is' : [9, 6, 2, 10]},
             {'gfg' : [5, 6, 7, 8], 'good' : [5, 7, 10]},
             {'gfg' : [7, 5], 'best' : [5, 7]}]
  
# printing original list
print("The original list is : " + str(test_list))
  
# frequency key 
freq_key = "gfg"
  
# Values frequencies of key
# Using Counter() + list comprehension
res = Counter([idx for val in test_list for idx in val[freq_key]])
  
# printing result 
print("The frequency dictionary : " + str(dict(res))) 

Output :

The original list is : [{‘gfg’: [1, 5, 6, 7], ‘is’: [9, 6, 2, 10]}, {‘gfg’: [5, 6, 7, 8], ‘good’: [5, 7, 10]}, {‘gfg’: [7, 5], ‘best’: [5, 7]}]
The frequency dictionary : {8: 1, 1: 1, 5: 3, 6: 2, 7: 3}

Method #2 : Using chain.from_iterables() + Counter()
The combination of above methods can be used to solve this problem. In this, we perform the task of iteration and binding using chain.from_iterables().

# Python3 code to demonstrate working of 
# Values frequencies of key
# Using chain.from_iterables() + Counter()
from collections import Counter
import itertools
  
# initializing list
test_list = [{'gfg' : [1, 5, 6, 7], 'is' : [9, 6, 2, 10]},
             {'gfg' : [5, 6, 7, 8], 'good' : [5, 7, 10]},
             {'gfg' : [7, 5], 'best' : [5, 7]}]
  
# printing original list
print("The original list is : " + str(test_list))
  
# frequency key 
freq_key = "gfg"
  
# Values frequencies of key
# Using chain.from_iterables() + Counter()
res = Counter(itertools.chain.from_iterable([sub[freq_key] for sub in test_list]))
  
# printing result 
print("The frequency dictionary : " + str(dict(res))) 

Output :

The original list is : [{‘gfg’: [1, 5, 6, 7], ‘is’: [9, 6, 2, 10]}, {‘gfg’: [5, 6, 7, 8], ‘good’: [5, 7, 10]}, {‘gfg’: [7, 5], ‘best’: [5, 7]}]
The frequency dictionary : {8: 1, 1: 1, 5: 3, 6: 2, 7: 3}

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Python – Values frequencies of key