Python: Remove duplicates from a list

Last update on April 19 2025 13:02:48 (UTC/GMT +8 hours)

Remove Duplicates from List

Write a Python program to remove duplicates from a list.

Visual Presentation:

Sample Solution:

Python Code:

# Define a list 'a' with some duplicate and unique elements
a = [10, 20, 30, 20, 10, 50, 60, 40, 80, 50, 40]

# Create an empty set to store duplicate items and an empty list for unique items
dup_items = set()
uniq_items = []

# Iterate through each element 'x' in the list 'a'
for x in a:
    # Check if the current element 'x' is not already in the set 'dup_items' (it's a duplicate check)
    if x not in dup_items:
        # If 'x' is not a duplicate, add it to the 'uniq_items' list
        uniq_items.append(x)
        # Add 'x' to the 'dup_items' set to mark it as a seen item
        dup_items.add(x)

# Print the set 'dup_items' which now contains the unique elements from the original list 'a'
print(dup_items)

Sample Output:

{40, 10, 80, 50, 20, 60, 30}

Explanation:

In the above exercise -

a = [10,20,30,20,10,50,60,40,80,50,40] -> Creates a list called a that contains 11 integers.

dup_items = set() -> Creates a new variable: an empty set called dup_items.

uniq_items = [] -> Creates a new variable: an empty list called uniq_items.

for x in a:
    if x not in dup_items:
        uniq_items.append(x)
        dup_items.add(x)

This line starts a 'for' loop that iterates over each element in the 'a' list, one at a time. The loop variable 'x' will take on the value of each element in the list during each iteration of the loop.

The if statement checks if the current element 'x' is not in the dup_items set. If this is true, it means the element is unique and should be added to the uniq_items list using the append method. Additionally, the element is added to the dup_items set using the add method to mark it as a duplicate.

print(dup_items) -> This line prints the 'dup_items' set to the console using the print() function. The expected output would be {40, 10, 80, 50, 20, 60, 30}

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to remove duplicates from a list while maintaining the order.
Write a Python program to find all unique elements from a list that appear only once.
Write a Python program to remove consecutive duplicate elements from a list.
Write a Python program to remove duplicate sublists from a list of lists.

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