Question

Write and test a function removeDuplicates(somelist) that removes duplicate values from a list.

Short answer

Use a set to track seen elements and build a list of unique items.

Step-by-step solution

Understand the Problem

We need a function, `removeDuplicates`, that takes a list as input and returns a new list with all duplicate values removed. The order of elements in the list should be preserved.

Define the Function

Create a Python function named `removeDuplicates` that accepts one parameter, `somelist`. Inside the function, you will define logic to remove duplicates while keeping the original order.

Initialize Data Structures

Inside the function, start by initializing an empty list called `unique_list` to store the elements without duplicates, and an empty set called `seen` to track elements that have already appeared.

Iterate Through the List

Use a for loop to iterate over each element in `somelist`. For each element, check if it is not in the `seen` set.

Check and Add Unique Elements

If the element is not in the `seen` set, append it to `unique_list` and add it to the `seen` set. This ensures that each element is added only once.

Return the Result

After the loop completes, return the `unique_list` which contains only the unique elements.

Test the Function

Test the function `removeDuplicates` with different lists including empty lists, lists with all unique elements, and lists with multiple duplicates. For example: `removeDuplicates([1, 2, 3, 2, 1, 4])` should return `[1, 2, 3, 4]`.

Key concepts

remove duplicates from list

In Python programming, removing duplicates from a list is a common task. Often, you need a clean list without any repeating elements. This can be necessary for data analysis, cleaning up user inputs, or merely organizing data. To achieve this, you identify and filter out elements that appear more than once, leaving you with a list containing only unique values. By keeping the order of elements as they first appeared, the `removeDuplicates` function is effective in maintaining the integrity of your data set.

Consider a list like `[1, 2, 3, 2, 1, 4]`. The goal is to transform it into `[1, 2, 3, 4]`. Doing so involves recognizing duplicates and ensuring they do not appear in the final list. Using data structures like a `set` helps keep track of what has already been encountered. This operation is useful because Python lists are ordered collections, and preserving this order is often desirable in applications.

function definition

Defining a function in Python is a pivotal part of programming. A function allows you to write a block of code and give it a name. You can call this block multiple times without repeating code. To define a function, use the `def` keyword followed by the function name and parentheses containing any parameters.

The `removeDuplicates` function is defined as `def removeDuplicates(somelist):`. This line tells Python you are creating a function named `removeDuplicates` that takes one parameter, `somelist`. Inside the function, any logic involving this list is implemented. Writing functions promotes code reusability and organization. Each function should do one specific task, making it easier to test and debug.

data structures

Data structures are essential in organizing and managing data efficiently within your code. In the process of removing duplicates from a list, two primary data structures come into play: lists and sets. Lists in Python are ordered and can hold multiple data types, making them flexible for iterative operations like filtering duplicates.

A set is a built-in Python data structure optimized for membership testing — it efficiently checks if an element is present. This feature makes sets ideal for tracking which elements have already been added to your list of unique items. Because sets automatically ignore duplicates, they complement the list structure by managing already-seen elements without redundancy.

list iteration

The concept of list iteration involves going through each element in a list to perform operations on them. This is a fundamental technique in programming, used for tasks like searching, modifying, or counting elements. In Python, the `for` loop is most often used for iteration.

In the `removeDuplicates` function, list iteration allows you to assess each element in `somelist` one by one. Using the `for` loop, you examine each element to determine if it has already been encountered as per the `seen` set. If not, the element is added to `unique_list`, and it also gets marked in `seen`, ensuring future duplicates are ignored. This method ensures that your final list contains only unique values while maintaining their original order in the input list.