Python: Remove duplicates from a list of integers, preserving order

Last update on April 17 2025 13:02:52 (UTC/GMT +8 hours)

Remove Duplicates, Preserve Order

Write a Python program to remove duplicates from a list of integers, preserving order.

Input:
[1, 3, 4, 10, 4, 1, 43]
Output:
[1, 3, 4, 10, 43]

Input:
[10, 11, 13, 23, 11, 25, 23, 76, 99]
Output:
[10, 11, 13, 23, 25, 76, 99]

Visual Presentation:

Sample Solution-1:

Python Code:

# Define a function named 'test' that takes a list of numbers as input and removes duplicates while preserving the original order
def test(nums):
    # Use a dictionary to convert the list to a set, effectively removing duplicates, and then convert it back to a list
    return list(dict.fromkeys(nums))

# Create a list of numbers named 'nums'
nums = [1, 3, 4, 10, 4, 1, 43]
# Print a message indicating the task and the original list of numbers
print("Original list of numbers:")
# Print the original list of numbers
print(nums)
# Print a message indicating the task and the result of the test function applied to 'nums'
print("Remove duplicates from the said list of integers, preserving order:")
# Print the result of the test function applied to 'nums'
print(test(nums))

# Create another list of numbers named 'nums'
nums = [10, 11, 13, 23, 11, 25, 23, 76, 99]
# Print a message indicating the task and the original list of numbers
print("\nOriginal list of numbers:")
# Print the original list of numbers
print(nums)
# Print a message indicating the task and the result of the test function applied to 'nums'
print("Remove duplicates from the said list of integers, preserving order:")
# Print the result of the test function applied to 'nums'
print(test(nums))

Sample Output:

Original list of numbers:
[1, 3, 4, 10, 4, 1, 43]
Remove duplicates from the said list of integers, preserving order:
[1, 3, 4, 10, 43]

Original list of numbers:
[10, 11, 13, 23, 11, 25, 23, 76, 99]
Remove duplicates from the said list of integers, preserving order:
[10, 11, 13, 23, 25, 76, 99]

Flowchart:

Sample Solution-2:

Python Code:

# Define a function named 'test' that takes a list of numbers as input and removes duplicates while preserving the original order
def test(nums):
    # Initialize an empty list named 'result' to store unique elements
    result = []
    # Iterate through each element 'x' in the input list 'nums'
    for x in nums:
        # Check if 'x' is not already present in the 'result' list
        if x not in result:
            # If not present, append 'x' to the 'result' list
            result.append(x)
    # Return the final list with duplicates removed
    return result
              
# Create a list of numbers named 'nums'
nums = [1, 3, 4, 10, 4, 1, 43]
# Print a message indicating the task and the original list of numbers
print("Original list of numbers:")
# Print the original list of numbers
print(nums)
# Print a message indicating the task and the result of the test function applied to 'nums'
print("Remove duplicates from the said list of integers, preserving order:")
# Print the result of the test function applied to 'nums'
print(test(nums))

# Create another list of numbers named 'nums'
nums = [10, 11, 13, 23, 11, 25, 23, 76, 99]
# Print a message indicating the task and the original list of numbers
print("\nOriginal list of numbers:")
# Print the original list of numbers
print(nums)
# Print a message indicating the task and the result of the test function applied to 'nums'
print("Remove duplicates from the said list of integers, preserving order:")
# Print the result of the test function applied to 'nums'
print(test(nums))

Sample Output:

Original list of numbers:
[1, 3, 4, 10, 4, 1, 43]
Remove duplicates from the said list of integers, preserving order:
[1, 3, 4, 10, 43]

Original list of numbers:
[10, 11, 13, 23, 11, 25, 23, 76, 99]
Remove duplicates from the said list of integers, preserving order:
[10, 11, 13, 23, 25, 76, 99]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to remove duplicate integers from a list while preserving the original order using an OrderedDict.
• Write a Python program to iterate over a list and add only unseen elements to a new list to remove duplicates.
• Write a Python program to filter out duplicates using a helper set and list comprehension while preserving order.
• Write a Python program to implement duplicate removal by manually checking for previous occurrences in the list.

Go to:

• Python Puzzles Exercises Home ↩
• Python Exercises Home ↩

Previous: Find the product of the units digits in the numbers.
Next: Find the numbers that are greater than 10 and have odd first and last digits.

Python Code Editor :

Have another way to solve this solution? Contribute your code (and comments) through Disqus.