Efficiently Dedupe List in Python

General Discussions
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1

How can I Python dedupe list efficiently? I need to check a list and remove all duplicates without specifying which items are duplicates. The goal is for the code to identify and remove duplicates automatically, keeping only one instance of each item, while preserving the original order.

For example, I have a list lseparatedOrbList with 12 items. One item is repeated six times, another is repeated five times, and there is only one instance of one item. I want the list to be reduced to only three unique items, maintaining their original order.

I tried the following code:

for i in lseparatedOrbList:
    for j in lseparatedOrbList:
        if lseparatedOrbList[i] == lseparatedOrbList[j]:
            lseparatedOrbList.remove(lseparatedOrbList[j])

But I got the error:

Traceback (most recent call last):
  File "qchemOutputSearch.py", line 123, in <module>
    for j in lseparatedOrbList:
NameError: name 'lseparatedOrbList' is not defined

I’m guessing this happens because I’m looping through lseparatedOrbList while modifying it. Can anyone suggest a more efficient and correct way to Python dedupe list without causing this error?

2

I’ve dealt with this kind of issue many times, and a clean approach I often use is leveraging a set for tracking duplicates. It’s efficient and preserves the order of items in your list.

Here’s how you can do it:

lseparatedOrbList = [1, 2, 2, 3, 4, 4, 5, 5, 5, 6]  
seen = set()  
unique_list = []  

for item in lseparatedOrbList:  
    if item not in seen:  
        unique_list.append(item)  
        seen.add(item)  

print(unique_list)  # Output: [1, 2, 3, 4, 5, 6]

This ensures a straightforward way to achieve Python dedupe list functionality without modifying the original list during iteration.

3

If you’re looking for an even more concise way to handle this, Python’s dict.fromkeys() method is a hidden gem. It works seamlessly for removing duplicates while maintaining the original order. This is thanks to dictionaries preserving insertion order in Python 3.7+.

Here’s the code:

lseparatedOrbList = [1, 2, 2, 3, 4, 4, 5, 5, 5, 6]  
unique_list = list(dict.fromkeys(lseparatedOrbList))  

print(unique_list)  # Output: [1, 2, 3, 4, 5, 6]

This approach is great if you want a clean one-liner solution for a Python dedupe list problem.

4

If you’re someone who enjoys combining logic and compactness, list comprehensions are a fantastic way to solve this. You can use a set within the comprehension for a streamlined solution.

Here’s how:

lseparatedOrbList = [1, 2, 2, 3, 4, 4, 5, 5, 5, 6]  
seen = set()  
unique_list = [item for item in lseparatedOrbList if not (item in seen or seen.add(item))]  

print(unique_list)  # Output: [1, 2, 3, 4, 5, 6]

This method is concise yet elegant and handles the Python dedupe list challenge effectively.