Reference library

Lists & loops

Iterate, transform, and combine sequences with readable loop patterns.

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Lists & loops easy

Intersection of Two Lists Preserving Order in Python

This code returns the common elements between two lists while preserving the order they appear in the first list, filtering out duplicates.

lists intersection order
Python 
def intersection_preserving_order(list1, list2):
    """
    Return the intersection of two lists while preserving the order
    of elements as they appear in list1.
    """
    set2 = set(list2)
    result = []
    seen = set()
    
    for item in list1:
        if item in set2 and item not in seen:
            resu…
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