Count the Sublists Containing given Element in a List - Python

Given a list of lists our task is to count the number of sublists containing the given element x. For example: li = [[1, 3, 5], [1, 3, 5, 7], [1, 3, 5, 7, 9]] and x = 1 then output will be 3.

Using List Comprehension

This method uses list comprehension to check for the presence of the given element in each sublist and uses sum() to count the occurrences.

li = [['a'], ['a', 'c', 'b'], ['d']]
x = 'a'

count = sum([x in sub_li for sub_li in li]) 

print(count)  

2

Explanation: We use list comprehension to check for x in each sublist and then use sum to count the True values (equivalent to 1).

Using a Loop (Naive Approach)

In this method we iterate through each sublist and check if the given element exists and if it does then a counter is incremented to keep track of the occurrences.

li = [['a'], ['a', 'c', 'b'], ['d']]
x = 'a'

c = 0
for sub in li:
    if x in sub:
        c += 1

print(c) 

2

Explanation: We iterate over each sublist in li and checks if x exists in that sublist or not then counter c is incremented for each match and the final value is printed.

Using chain.from_iterable and Counter

In this approach, we use chain from itertools and Counter from collections to count occurrences of x across flattened sublists.

from itertools import chain
from collections import Counter

li = [['a'], ['a', 'c', 'b'], ['d']]
x = 'a'

c = Counter(chain.from_iterable(set(sub) for sub in li))[x]

print(c) 

2

Explanation:

• set(sub) ensures each sublist is treated as a unique collection of elements which prevents duplicate counts within the same sublist.
• chain.from_iterable() combines these sets into a single sequence which is used by Counter to count occurrences of x.

Using reduce()

This approach uses the reduce() function from the functools module to iteratively count how many sublists contain the given element.

from functools import reduce

li = [[1, 3, 5], [1, 3, 5, 7], [1, 3, 5, 7, 9]]
x = 1

count = reduce(lambda total, sublist: total + (1 if x in sublist else 0), li, 0)

print(count) 

3

Explanation:

• reduce() accumulates the count by iterating over each sublist and updating the total by adding 1 if x is found in the sublist, otherwise adding 0.
• lambda function checks if x exists in the sublist and adds 1 if true, else adds 0.