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Python – Ways to remove duplicates from list

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  • Difficulty Level : Easy
  • Last Updated : 25 Jul, 2022

This article focuses on one of the operations of getting the unique list from a list that contains a possible duplicated. Remove duplicates from list operation has a large number of applications and hence, its knowledge is good to have. 

Method 1: Using *set() 

This is the fastest and smallest method to achieve a particular task. It first removes the duplicates and returns a dictionary which has to be converted to list. 

Python3




# Python 3 code to demonstrate
# removing duplicate elements from the list
l = [1, 2, 4, 2, 1, 4, 5]
print("Original List: ", l)
res = [*set(l)]
print("List after removing duplicate elements: ", res)

Output:

Original list: [1, 2, 4, 2, 1, 4, 5]
List after removing duplicate elements: [1, 2, 4, 5]

Method 2: Using list comprehension 

This method has working similarly to the above method, but this is just a one-liner shorthand of a longer method done with the help of list comprehension.  

Python3




# Python 3 code to demonstrate
# removing duplicated from list
# using list comprehension
 
# initializing list
test_list = [1, 3, 5, 6, 3, 5, 6, 1]
print (& quot
        The original list is : & quot
        + str(test_list))
 
# using list comprehension
# to remove duplicated
# from list
res = []
[res.append(x) for x in test_list if x not in res]
 
# printing list after removal
print (& quot
        The list after removing duplicates : & quot
        + str(res))

Output :

The original list is : [1, 3, 5, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 3, 5, 6]

Method 3: Using set()

This is the most popular way by which the duplicates are removed from the list. But the main and notable drawback of this approach is that the ordering of the element is lost in this particular method.  

Python3




# Python 3 code to demonstrate
# removing duplicated from list
# using set()
 
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print (& quot
        The original list is : & quot
        + str(test_list))
 
# using set()
# to remove duplicated
# from list
test_list = list(set(test_list))
 
# printing list after removal
# distorted ordering
print (& quot
        The list after removing duplicates : & quot
        + str(test_list))

Output :

The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 3, 5, 6]

Method 4: Using list comprehension + enumerate() 

list comprehension coupled with enumerate function can also achieve this task. It basically looks for already occurred elements and skips adding them. It preserves the list ordering.  

Python3




# Python 3 code to demonstrate
# removing duplicated from list
# using list comprehension + enumerate()
 
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print (& quot
        The original list is : & quot
        + str(test_list))
 
# using list comprehension + enumerate()
# to remove duplicated
# from list
res = [i for n, i in enumerate(test_list) if i not in test_list[:n]]
 
# printing list after removal
print (& quot
        The list after removing duplicates : & quot
        + str(res))

Output :

The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 5, 3, 6]

Method 5: Using collections.OrderedDict.fromkeys()

This is the fastest method to achieve a particular task. It first removes the duplicates and returns a dictionary which has to be converted to list. This works well in case of strings also.  

Python3




# Python 3 code to demonstrate
# removing duplicated from list
# using collections.OrderedDict.fromkeys()
from collections import OrderedDict
 
# initializing list
test_list = [1, 5, 3, 6, 3, 5, 6, 1]
print (& quot
        The original list is : & quot
        + str(test_list))
 
# using collections.OrderedDict.fromkeys()
# to remove duplicated
# from list
res = list(OrderedDict.fromkeys(test_list))
 
# printing list after removal
print (& quot
        The list after removing duplicates : & quot
        + str(res))

Output:

The original list is : [1, 5, 3, 6, 3, 5, 6, 1]
The list after removing duplicates : [1, 5, 3, 6]

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