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Python – Specific Characters Frequency in String List
  • Last Updated : 05 Sep, 2020

Given String list, extract frequency of specific characters in whole strings list.

Input : test_list = [“geeksforgeeks is best for geeks”], chr_list = [‘e’, ‘b’, ‘g’, ‘f’]
Output : {‘g’: 3, ‘e’: 7, ‘b’: 1, ‘f’ : 1}
Explanation : Frequency of certain characters extracted.

Input : test_list = [“geeksforgeeks], chr_list = [‘e’, ‘g’]
Output : {‘g’: 2, ‘e’: 4}
Explanation : Frequency of certain characters extracted.

Method #1 : Using join() + Counter()

In this, we concatenate all the strings, and then Counter() performs task of getting all frequencies. Last step is to get only specific characters from List in dictionary using dictionary comprehension.



Python3




# Python3 code to demonstrate working of 
# Specific Characters Frequency in String List
# Using join() + Counter()
from collections import Counter
  
# initializing lists
test_list = ["geeksforgeeks is best for geeks"]
  
# printing original list
print("The original list : " + str(test_list))
  
# char list 
chr_list = ['e', 'b', 'g']
  
# dict comprehension to retrieve on certain Frequencies
res = {key:val for key, val in dict(Counter("".join(test_list))).items() if key in chr_list}
      
# printing result 
print("Specific Characters Frequencies : " + str(res))
Output
The original list : ['geeksforgeeks is best for geeks']
Specific Characters Frequencies : {'g': 3, 'e': 7, 'b': 1}

Method #2 : Using chain.from_iterable() + Counter() + dictionary comprehension

In this, task of concatenation is done using chain.from_iterable() rather than join(). Rest all tasks are done as above method.

Python3




# Python3 code to demonstrate working of 
# Specific Characters Frequency in String List
# Using chain.from_iterable() + Counter() + dictionary comprehension
from collections import Counter
from itertools import chain
  
# initializing lists
test_list = ["geeksforgeeks is best for geeks"]
  
# printing original list
print("The original list : " + str(test_list))
  
# char list 
chr_list = ['e', 'b', 'g']
  
# dict comprehension to retrieve on certain Frequencies
# from_iterable to flatten / join
res = {key:val for key, val in dict(Counter(chain.from_iterable(test_list))).items() if key in chr_list}
      
# printing result 
print("Specific Characters Frequencies : " + str(res))
Output
The original list : ['geeksforgeeks is best for geeks']
Specific Characters Frequencies : {'g': 3, 'e': 7, 'b': 1}

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