Python | Unique List Values Filtering

Introduction

In Python, a list is a collection of items that are ordered and changeable. Sometimes, we need to filter out the unique values from a list. In this challenge, you are required to write a Python function that takes a list as an argument and returns a new list with only the non-unique values.

Filter Unique List Values

Write a Python function called filter_unique(lst) that takes a list as an argument and returns a new list with only the non-unique values. To solve this problem, you can follow these steps:

Use collections.Counter to get the count of each value in the list.
Use a list comprehension to create a list containing only the non-unique values.

Your function should satisfy the following requirements:

The function should take a list as an argument.
The function should return a new list with only the non-unique values.
The function should not modify the original list.
The function should be case-sensitive, meaning that 'a' and 'A' are considered different values.

def filter_unique(lst):
    ## your code here

from collections import Counter

def filter_unique(lst):
  return [item for item, count in Counter(lst).items() if count > 1]

filter_unique([1, 2, 2, 3, 4, 4, 5]) ## [2, 4]

Summary

In this challenge, you have learned how to filter out the unique values from a list using Python. You have also learned how to use collections.Counter to count the occurrences of each value in a list and how to use a list comprehension to create a new list with only the non-unique values.