How to Remove Adjacent Duplicates in a Python List: 5 Simple Methods

1. Introduction

Hello everyone, I am Pipi. A few days ago a question was asked in the Python community group "Chloe" about processing a list to remove adjacent duplicate values. The original data is:

origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]

The expected result is:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 4]

2. Implementation

Method 1

Using itertools.groupby:

import itertools
origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]
final_lst = [x[0] for x in itertools.groupby(origin_lst)]
print(final_lst)

Method 2

Using a list comprehension with index checking:

origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]
res = [origin_lst[i] for i in range(len(origin_lst)) if i == 0 or origin_lst[i] != origin_lst[i - 1]]
print(res)

Method 3

Using a simple loop:

origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]
result = [origin_lst[0]]
for i in range(1, len(origin_lst)):
    if origin_lst[i] != origin_lst[i-1]:
        result.append(origin_lst[i])
print(result)

Method 4

Using a generator function:

origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]

def del_adjacent(iterable):
    prev = object()
    for item in iterable:
        if item != prev:
            prev = item
            yield item

result = list(del_adjacent(origin_lst))
print(result)

Method 5

Using enumerate:

origin_lst = [0, 0, 1, 2, 3, 4, 4, 5, 6, 6, 6, 7, 8, 9, 4, 4]

lst_final = []
for index, val in enumerate(origin_lst):
    if val != origin_lst[index - 1]:
        lst_final.append(val)
print(lst_final)

3. Summary

This article presented a Python data‑processing problem and offered multiple concrete solutions—using itertools.groupby, list comprehensions, simple loops, a generator, and enumerate —to help fans successfully remove adjacent duplicates from a list.

Thanks to the contributors who provided the ideas and code.