nunique() for cardinality in Data Analysis Python - Mini Project: Build & Apply

Counting Unique Values with nunique() for Cardinality

📖 Scenario: You work in a small bookstore. You have a list of books sold each day. You want to find out how many different book titles were sold.

🎯 Goal: Build a small program that counts the number of unique book titles sold using the nunique() method.

📋 What You'll Learn

Create a pandas DataFrame with a column named book_title containing the exact book titles sold.

Create a variable called unique_books_count to store the number of unique book titles using nunique().

Print the value of unique_books_count.

💡 Why This Matters

🌍 Real World

Counting unique items sold helps businesses understand product variety and customer preferences.

💼 Career

Data analysts often count unique values to summarize data and find important insights.

1

Create the sales data

Create a pandas DataFrame called sales_data with one column named book_title. The column should have these exact values in this order: 'The Alchemist', '1984', 'The Alchemist', 'Brave New World', '1984'.

Data Analysis Python

# Create the sales_data DataFrame with the book_title column
# Your code here

Need a hint?

Use pd.DataFrame with a dictionary where the key is 'book_title' and the value is the list of book titles.

2

Set up the variable for unique count

Create a variable called unique_books_count and set it to the number of unique book titles in sales_data['book_title'] using the nunique() method.

Data Analysis Python

import pandas as pd

sales_data = pd.DataFrame({
    'book_title': ['The Alchemist', '1984', 'The Alchemist', 'Brave New World', '1984']
})

# Create unique_books_count using nunique()
# Your code here

Need a hint?

Use sales_data['book_title'].nunique() to count unique titles.

3

Print the number of unique book titles

Write a print() statement to display the value of unique_books_count.

Data Analysis Python

import pandas as pd

sales_data = pd.DataFrame({
    'book_title': ['The Alchemist', '1984', 'The Alchemist', 'Brave New World', '1984']
})

unique_books_count = sales_data['book_title'].nunique()

# Print unique_books_count
# Your code here

Need a hint?

Use print(unique_books_count) to show the result.

4

Explain the result

Add a print statement that shows a friendly message: print(f"Number of unique books sold: {unique_books_count}").

Data Analysis Python

import pandas as pd

sales_data = pd.DataFrame({
    'book_title': ['The Alchemist', '1984', 'The Alchemist', 'Brave New World', '1984']
})

unique_books_count = sales_data['book_title'].nunique()

print(unique_books_count)

# Print a friendly message with the count
# Your code here

Need a hint?

Use an f-string inside print() to show the message with the count.