Python – Consecutive identical elements count

When working with lists in Python, you might need to count how many distinct values appear consecutively (repeated adjacent elements). This can be achieved using iteration, the append() method, and set() to find unique consecutive elements.

Example

Here's how to count distinct consecutive identical elements in a list ?

my_list = [24, 24, 24, 15, 15, 64, 64, 71, 13, 95, 100]

print("The list is :")
print(my_list)

my_result = []
for index in range(0, len(my_list) - 1):
    if my_list[index] == my_list[index + 1]:
        my_result.append(my_list[index])

my_result = len(list(set(my_result)))

print("The result is :")
print(my_result)

The list is :
[24, 24, 24, 15, 15, 64, 64, 71, 13, 95, 100]
The result is :
3

How It Works

The algorithm works as follows ?

• A list is defined and displayed on the console.

• An empty list is created to store consecutive identical elements.

• The list is iterated, comparing each element with the next one. If they are equal, the current element is added to the result list.

• The result list is converted to a set (removing duplicates) and back to a list, then its length gives the count of distinct consecutive identical elements.

• In this example, elements 24, 15, and 64 appear consecutively, so the result is 3.

Alternative Method Using itertools.groupby()

A more elegant approach uses itertools.groupby() to group consecutive identical elements ?

from itertools import groupby

my_list = [24, 24, 24, 15, 15, 64, 64, 71, 13, 95, 100]

print("The list is :")
print(my_list)

consecutive_groups = [list(group) for key, group in groupby(my_list)]
consecutive_identical = [group for group in consecutive_groups if len(group) > 1]

print("Consecutive identical groups:")
print(consecutive_identical)
print("Count of distinct consecutive identical elements:")
print(len(consecutive_identical))

The list is :
[24, 24, 24, 15, 15, 64, 64, 71, 13, 95, 100]
Consecutive identical groups:
[[24, 24, 24], [15, 15], [64, 64]]
Count of distinct consecutive identical elements:
3

Conclusion

Both methods effectively count distinct consecutive identical elements. The first approach uses basic iteration and set operations, while itertools.groupby() provides a more readable and efficient solution for grouping consecutive elements.