4 ways to Get Unique values from a list in Python

There are a lot of use cases in python programming where we would require to fetch unique values from a list.

If stuck with this problem Don’t worry ! We got you covered.

In this article we will discuss briefly about the different methods fetching unique values from a list in Python language.

Overview of Lists in Python

List contains a group of elements of a different data type separated by commas, and enclosed inside square brackets [ ].
Example of a list:

sample_list = [1,2,5,2,6,1,4,3,6,3,9,8,2]

Methods to fetch Unique values from a Python List

There are a lot of cases wherein we would be required to get unique values from a list.

Therefore, lets dive deep into the different methods

Using the for loop and a new list

Starting with the most basic and simplest method, we can simply use a for loop and a new list to solve this problem.

We can simply iterate through the existing python list and append the unique values on to a new empty list.

This is the novice method for solving this and probably preferred by the beginners.

sample_list = [1,2,5,2,6,1,4,3,6,3,9,8,2]
unique_list = []
for element in sample_list:
    if element not in unique_list:
        unique_list.append(element)

print(unique_list)

Output:

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

Pretty Simple and easy method.

But if you are enthusiastic about programming, then this is not for you.

Using python set() method

Sets are a unique kind of Data structures in Python.

They have a property that they allow only one occurrence of each element and thus are a sequential memory location of only unique values.

Thus, converting the python list to set using set() method in order to fetch only unique values and then converting the set to the list using list().

sample_list = [1,2,5,2,6,1,4,3,6,3,9,8,2]

unique_list = list(set(sample_list))
print(unique_list)

Output:

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

This would also improve the runtime performance and thus is a good approach for this problem.

But this method has a small disadvantage i.e. it doesn’t preserve the order of elements in the output.

Using numpy.unique method

If you don’t belong to Python background, then Numpy might sound very unfamiliar to you.

But don’t worry, it’s just like any other module in python like collections, os etc. by the help of which we can simplify our problems.

We have to explicitly import the modules before using them inside of our program.

Using this methods consists of two parts, first being to convert the list into a numpy array and then using numpy.unique, which returns a list of only unique values from the list.

import numpy as numpy

sample_list = [1,2,5,2,6,1,4,3,6,3,9,8,2]
arr = numpy.array(sample_list)
unique_list = numpy.unique(arr)

print(unique_list)

Output:

[1 2 3 4 5 6 8 9]

This method returns a sorted list containing all the unique values from the list.

Using the python Counter() method

If we are using explicitly calling a module for our use case, then why not using our favorite collections module.

The collections module contains a method called Counter() which prints all the unique values from the input list.

We can carry out this functionality with the help of * operator.

from collections import Counter

sample_list = [1,2,5,2,6,1,4,3,6,3,9,8,2]
print(*Counter(sample_list))

Output:

1 2 5 6 4 3 9 8

This method returns a sequence of unique values from the list, but not necessarily a list.

Conclusion

In this article we discussed about the various methods by the help of which we can get the unique values from a python list.

We started off by discussing the novice method and then slowly increasing the complexity of the code by using external python modules and classes.

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I am Dibyanshu Mohanty, Undergraduate Engineering Student at VIT, Vellore with a keen interest in Web and App Development

https://python.shiksha/authors/dmohanty/