Python – Element frequencies in percent range

Given a list of elements, and percent ranges, the task is to write a python program to extract all the elements whose frequency is present in a given range. 

Input : test_list = [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8], strt, end = 13, 25

Output : [6, 7, 8]

Explanation : 21.4, 14.2, 14.2 is percentage presence of 6, 7, 8 respectively.

Input : test_list = [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8], strt, end = 13, 20

Output : [7, 8]

Explanation : 14.2, 14.2 is percentage presence of 7, 8 respectively.

Presence percentage can be simply computed by the below formula:

Frequency of the element present in the list/ total no. of elements in the list

Method #1 : Using Counter() + set() + loop + len()

In this, frequencies of all the elements are extracted using loop. Next step is to get the set of elements of list and check if frequencies are between range specified.

Python3

# Python3 code to demonstrate working of
# Element frequencies in percent range
# Using Counter() + set() + loop + len()
from collections import Counter

# initializing list
test_list = [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8]

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

# initializing percent ranges
strt, end = 13, 25

# getting frequencies
freqs = dict(Counter(test_list))

# computing percents and assigning
res = []
for ele in set(test_list):
    percent = (freqs[ele] / len(test_list)) * 100
    if percent >= strt and percent <= end:
        res.append(ele)

# printing result
print("Elements within range of frequencies : " + str(res))

Output:

The original list is : [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8]
Elements within range of frequencies : [6, 7, 8]

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #2 : Using Counter() + loop + len()
This performs tasks in an almost similar manner, the key difference being the Counter keys are iterated rather than the list elements, as they’d provide similar output. 

Python3

# Python3 code to demonstrate working of
# Element frequencies in percent range
# Using Counter() + loop + len()
from collections import Counter

# initializing list
test_list = [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8]

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

# initializing percent ranges
strt, end = 13, 25

# getting frequencies
freqs = dict(Counter(test_list))

# computing percents and assigning
# iterating from dictionary
res = []
for ele in freqs:
    percent = (freqs[ele] / len(test_list)) * 100
    if percent >= strt and percent <= end:
        res.append(ele)

# printing result
print("Elements within range of frequencies : " + str(res))

Output:

The original list is : [4, 6, 2, 4, 6, 7, 8, 4, 9, 1, 4, 6, 7, 8]
Elements within range of frequencies : [6, 7, 8]

Time complexity: O(n*n), where n is the length of the test_list. The Counter() + loop + len() takes O(n*n) time
Auxiliary Space: O(n), extra space of size n is required