Python – Fractional Frequency of elements in List

Given a List, get fractional frequency of each element at each position.

Input : test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4] 
Output : [‘1/4’, ‘1/3’, ‘2/4’, ‘1/1’, ‘1/1’, ‘2/3’, ‘3/4’, ‘3/3’, ‘4/4’] 
Explanation : 4 occurs 1/4th of total occurrences till 1st index, and so on.
Input : test_list = [4, 5, 4, 6, 7, 5] 
Output : [‘1/2’, ‘1/2’, ‘2/2’, ‘1/1’, ‘1/1’, ‘2/2’] 
Explanation : 4 occurs 1/2th of total occurrences till 1st index, and so on. 

Method : Using Counter() + loop + dictionary comprehension

In this, we use Counter() to get the frequency of each element in list and to form denominator part of fraction. Numerator is initialized to 0 for each element. Then loop is used to add the elements in numerator and join with total frequency in denominator.

Python3

# Python3 code to demonstrate working of
# Fractional Frequency of elements in List
# Using Counter() + loop + dictionary comprehension
from collections import Counter

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]

# printing original list
print("The original list is : " + str(test_list))

# initializing numerator
number = {idx : 0 for idx in set(test_list)}

# initializing denominator
denom = Counter(test_list)

res = []
for ele in test_list:

    # increasing counter
    number[ele] += 1
    res.append(str(number[ele]) + '/' + str(denom[ele]))

# printing result
print("Fractional Frequency List : " + str(res))

Output

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]
Fractional Frequency List : ['1/5', '1/3', '2/5', '1/3', '1/1', '2/3', '3/5', '3/3', '4/5', '2/3', '5/5', '3/3']

Time Complexity: O(n*n), where n is the length of the input list. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”. 

Method : Using list(),set(),count() methods

Approach

1. Create a dictionary with unique values of list as keys and values as their occurences in original list (using list(),set(),count()) methods
2. Initiate a for loop to traverse the original list to append the fractional frequency of output list(using count())
3. Display output list

Python3

# Python3 code to demonstrate working of
# Fractional Frequency of elements in List

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]

# printing original list
print("The original list is : " + str(test_list))

x=list(set(test_list))
d=dict()
for i in x:
    d[i]=test_list.count(i)
res=[]
for i in range(0,len(test_list)):
    a=test_list[:i+1].count(test_list[i])
    res.append(str(a)+"/"+str(d[test_list[i]]))
# printing result
print("Fractional Frequency List : " + str(res))

Output

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]
Fractional Frequency List : ['1/5', '1/3', '2/5', '1/3', '1/1', '2/3', '3/5', '3/3', '4/5', '2/3', '5/5', '3/3']

Time Complexity: O(n*n), where n is the length of the input list. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”.

Method : Using numpy:

Algorithm:

1. Initialize an empty list “freq_list”.
2. Find the unique values and their respective counts in the given list “test_list” using numpy’s unique() method.
3. For each unique value, get the indices where the value occurs in “test_list” using numpy’s where() method.
4. For each index of the unique value, calculate the fractional frequency by dividing the count of the value by the number of times it occurs in the sublist from the start of “test_list” up to the current index.
5. Append the fractional frequency to the “freq_list”.
6. Print the “freq_list”.

Python3

import numpy as np

test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]

print("The original list is : " + str(test_list))

unique_vals, counts = np.unique(test_list, return_counts=True)
freq_list = []

for val, count in zip(unique_vals, counts):
    indices = np.where(test_list == val)[0]
    for i in range(len(indices)):
        freq_list.append(
            "{}/{}".format(np.count_nonzero(test_list[:indices[i]+1] == val), count))

print("Fractional Frequency List : " + str(freq_list))

# This code is contributed by Jyothi Pinjala

Output:

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]
Fractional Frequency List : ['1/5', '2/5', '3/5', '4/5', '5/5', '1/3', '2/3', '3/3', '1/3', '2/3', '3/3', '1/1']

Time Complexity: O(n^2), where n is the length of the input list. The worst-case scenario occurs when all the elements of the list are unique and the nested loop runs n times for each element.

Space Complexity: O(n), where n is the length of the input list. The space required by the “freq_list” increases linearly with the length of the input list.

Method : Using list(), set(), operator.countOf() methods:

Approach:

1. Create a dictionary with unique values of the list as keys and values as their occurrences in the original list (using list(),set(),operator.countOf()) methods.
2. Initiate a for loop to traverse the original list to append the fractional frequency of output list(using operator.countOf()).
3. Display the output list.

Below is the implementation of the above approach:

Python3

# Python3 code to demonstrate working of
# Fractional Frequency of elements in List
import operator

# initializing list
test_list = [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]

# printing original list
print("The original list is : " + str(test_list))

x = list(set(test_list))
d = dict()

for i in x:
    d[i] = operator.countOf(test_list, i)

res = []

for i in range(0, len(test_list)):
    a = operator.countOf(test_list[:i+1], test_list[i])
    res.append(str(a)+"/"+str(d[test_list[i]]))

# Print the result
print("Fractional Frequency List : " + str(res))

Output

The original list is : [4, 5, 4, 6, 7, 5, 4, 5, 4, 6, 4, 6]
Fractional Frequency List : ['1/5', '1/3', '2/5', '1/3', '1/1', '2/3', '3/5', '3/3', '4/5', '2/3', '5/5', '3/3']

Time Complexity: O(n*n), where n is the length of the input list. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”.