List Product Excluding Duplicates - Python

The task of finding the product of unique elements in a list involves identifying and multiplying only the distinct values, effectively excluding any duplicates. For example, if a = [1, 3, 5, 6, 3, 5, 6, 1], the unique elements would be {1, 3, 5, 6}, and the product of these values would be 90.

Using set()

set() automatically removes duplicates because sets do not allow duplicate elements. By converting the list to a set, we can efficiently filter out repeated values and then compute the product of the unique elements. This approach is simple and works well for most cases.

a = [1, 3, 5, 6, 3, 5, 6, 1]

# Unique Elements
b = set(a) # Convert `a` to set
res = 1 # initialize res to 1

for i in b:
    res *= i

print(str(res))

90

Explanation: for loop iterates through each element in the set unique_elements. During each iteration, the value of res is multiplied by the current element i , updating the product. The loop computes the product as 1 * 3 * 5 * 6, which results in 90.

Using dict.fromkeys()

dict.fromkeys() creates a dictionary with list elements as keys, which inherently removes any duplicates. This method is straightforward and easy to understand, offering a readable way to filter out duplicates and calculate the product of unique values while maintaining the order of insertion.

a = [1, 3, 5, 6, 3, 5, 6, 1]

# Unique Elements
b = dict.fromkeys(a)  # Remove duplicates using dictionary keys
res = 1 # initialize res to 1

for i in unique_val:
    res *= i

print(str(res))

90

Explanation :for loop iterates over the keys of the dictionary and multiplies res by each key. The product is calculated as 1 * 3 * 5 * 6, which gives 90.

Using Counter

Counter class from the collections module is typically used for counting occurrences of elements. By extracting the keys from the Counter object, we can get the unique elements. This method is helpful when we also need frequency information, though it can be used just to filter duplicates and compute the product of the unique numbers.

from collections import Counter

a = [1, 3, 5, 6, 3, 5, 6, 1]

# Unique Values
b = Counter(a)  # Count frequency of elements
res = 1 # initialize res to 1

for i in b:
    res *= i

print(str(res))

90

Explanation: for loop iterates through the keys of the Counter object. In each iteration, res is multiplied by the current element. The product is calculated as 1 * 3 * 5 * 6, resulting in 90.

Using in keyword

In this approach, a for loop iterates through the list and the in keyword is used to check if an element has already been added to a separate list of unique elements. This method is easy to implement but can become slower with larger lists due to the repeated checks.

a = [1, 3, 5, 6, 3, 5, 6, 1]

# Unique Elements
b = []
for i in a:
    if i not in b:
        b.append(i)

res = 1 # initialize res to 1
for i in b:
    res *= i

print(str(res))

90

Explanation: for loop iterates over each element in the list a, appending it to unique_elements if it's not already present. This ensures only unique elements are stored. Another for loop iterates through unique_elements, multiplying res by each element.