Python - Total equal pairs in List

When it is required to find the total equal pairs in a list, we can use the set() function along with the floor division operator // and iteration. This approach counts how many pairs can be formed from duplicate elements in the list.

Example

Below is a demonstration of finding equal pairs in a list −

numbers = [34, 56, 12, 32, 78, 99, 67, 34, 52, 78, 99, 10, 0, 11, 23, 9]
print("The list is :")
print(numbers)

unique_elements = set(numbers)
total_pairs = 0

for element in unique_elements:
    total_pairs += numbers.count(element) // 2

print("The total pairs are :")
print(total_pairs)

Output

The list is :
[34, 56, 12, 32, 78, 99, 67, 34, 52, 78, 99, 10, 0, 11, 23, 9]
The total pairs are :
3

How It Works

The algorithm works by following these steps −

• Convert the list to a set to get unique elements, eliminating duplicates for iteration

• For each unique element, count its occurrences in the original list using count()

• Use floor division // by 2 to find how many pairs can be formed from that element

• Sum up all the pairs from different elements to get the total

Alternative Method Using Counter

You can also use Python's Counter from the collections module for a more efficient approach −

from collections import Counter

numbers = [34, 56, 12, 32, 78, 99, 67, 34, 52, 78, 99, 10, 0, 11, 23, 9]
print("The list is :")
print(numbers)

element_counts = Counter(numbers)
total_pairs = sum(count // 2 for count in element_counts.values())

print("The total pairs are :")
print(total_pairs)

The list is :
[34, 56, 12, 32, 78, 99, 67, 34, 52, 78, 99, 10, 0, 11, 23, 9]
The total pairs are :
3

Conclusion

Use the set-based approach for simple cases or Counter for better performance with large lists. Both methods use floor division to count pairs effectively from duplicate elements.