Guillaume Redoulès

Extracting unique values from a list or an array

  2. Python
  3. Basics

Using lists

An easy way to extract the unique values of a list in python is to convert the list to a set. A set is an unordered collection of items. Every element is unique (no duplicates) and must be immutable. 

my_list = [10, 20, 30, 40, 20, 50, 60, 40]
print(f"Original List : {my_list}")

my_set = set(my_list)
my_new_list = list(my_set) # the set is converted back to a list with the list() function
print(f"List of unique numbers : {my_new_list}")

Original List : [10, 20, 30, 40, 20, 50, 60, 40]
List of unique numbers : [40, 10, 50, 20, 60, 30]

Using numpy

If you are using numpy you can extract the unique values of an array with the unique function builtin numpy:

import numpy as np
arr = np.array(my_list)
print(f'Initial numpy array : {arr}\n')


unique_arr = np.unique(arr)
print(f'Numpy array with unique values : {unique_arr}')

Initial numpy array : [10 20 30 40 20 50 60 40]

Numpy array with unique values : [10 20 30 40 50 60]