Tutorial

Python Remove Duplicates from a List

Published on August 3, 2022
author

Pankaj

Python Remove Duplicates from a List

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There are many ways to remove duplicates from a Python List.

Removing Duplicates from a List

Python list can contain duplicate elements. Let’s look into examples of removing the duplicate elements in different ways.

1. Using Temporary List

This is the brute-force way to remove duplicate elements from a list. We will create a temporary list and append elements to it only if it’s not present.

ints_list = [1, 2, 3, 4, 3, 2]

temp = []

for x in ints_list:
    if x not in temp:
        temp.append(x)

ints_list = temp

print(f'Updated List after removing duplicates = {temp}')

Output: Updated List after removing duplicates = [1, 2, 3, 4] Recommended Reading: Python f-strings

2. set() function

Python set doesn’t have duplicate elements. We can use the built-in set() function to convert the list to a set, then use the list() function to convert it back to the list.

ints_list = [1, 2, 3, 4, 3, 2]

ints_list1 = list(set(ints_list))
print(ints_list1)  # [1, 2, 3, 4]

3. List elements as Dictionary Keys

We know that dictionary keys are unique. The dict class has fromkeys() function that accepts an iterable to create the dictionary with keys from the iterable.

ints_list = [1, 2, 3, 4, 3, 2]

ints_list2 = list(dict.fromkeys(ints_list))
print(ints_list2)  # [1, 2, 3, 4]

The list count() method returns the number of occurrences of the value. We can use it with the remove() method to eliminate the duplicate elements from the list.

ints_list = [1, 2, 3, 4, 3, 2]

for x in ints_list:
    if ints_list.count(x) > 1:
        ints_list.remove(x)
print(ints_list)  # [1, 2, 3, 4]

NOTE: As pointed out in the below comment, using the count() function is not advisable while removing the element from the same iterator because it can lead to unwanted results. For example:

values = [87, 94, 45, 94, 94, 41, 65, 94, 41, 99, 94, 94, 94]

for x in values:
    if values.count(x) > 1:
        values.remove(x)
print(values)  # [87, 45, 65, 41, 99, 94, 94] - 94 is still present twice

5. List Comprehension

We can create a list from an iterable using the list comprehension. This technique is the same as using the temporary list and the for loop to remove the duplicate elements. But, it reduces the number of lines of the code.

int_list = [1, 2, 3, 4, 3, 2]
temp = []
[temp.append(x) for x in ints_list if x not in temp]
print(temp)  # [1, 2, 3, 4]

Best Way to Remove Duplicates from a List

If you don’t want duplicate elements, you should use Set. But, if you have to remove the duplicate values from a list, then I would prefer count() function because it doesn’t create another temporary set or list object. So, it’s more memory efficient.

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JournalDev
DigitalOcean Employee
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December 22, 2020

values = [87, 94, 45, 94, 94, 41, 65, 94, 41, 99, 94, 94, 94] def removeDuplicate(z): for i in z: if z.count(i)>1: z.remove(i) removeDuplicate(z) return z print(removeDuplicate(values)) ************Output************** [87, 45, 65, 41, 99, 94]

- vikram ram raut

    JournalDev
    DigitalOcean Employee
    DigitalOcean Employee badge
    December 2, 2020

    The count() method should never be used. The reason is you should never try to remove an element from a list while iterating on the list itself. The system may behave unexpectedly and skip over a particular item from the list as the list is constantly changing while the loop runs. Try the count() method on following list: values = [87, 94, 45, 94, 94, 41, 65, 94, 41, 99, 94, 94, 94] You’ll notice that the value 94 still stays in the final outcome. The best way is to use set method.

    - Meet

      JournalDev
      DigitalOcean Employee
      DigitalOcean Employee badge
      June 27, 2020

      how can i remove duplicates using two for loop by comparing the list member and if match occur then simply remove the particular element

      - RANA SIDHDHARAJSINH SAHDEVSINH

        JournalDev
        DigitalOcean Employee
        DigitalOcean Employee badge
        May 28, 2020

        ints_list = [1,1,1,1] for x in ints_list: if ints_list.count(x) > 1: ints_list.remove(x) print(ints_list) # Output: [1,1]

        - chirag maliwal

          JournalDev
          DigitalOcean Employee
          DigitalOcean Employee badge
          May 7, 2020

          how can i remove duplicate from a list without using a for loop or while loop or any in-build function in python do’not use list comprehension as well.

          - Rajeev

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