How to Remove Adjacent Duplicates from a Python List – 5 Simple Methods

Introduction

A user asked how to process a list in Python so that consecutive duplicate values are collapsed, expecting the result [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 4] from the original data

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

.

Implementation

Method 1 (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)

Running this code produces the expected output.

Method 2 (list comprehension)

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)

The result matches the expectation.

Method 3 (explicit 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)

The output is correct.

Method 4 (generator)

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)

The generator also yields the desired list.

Method 5 (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)

This approach also produces the correct result.

Conclusion

The article presented multiple ways to eliminate adjacent duplicates in a Python list, demonstrating that there are many viable solutions to this common data‑processing problem.