Book Image

Python Data Cleaning Cookbook

By : Michael Walker
Book Image

Python Data Cleaning Cookbook

By: Michael Walker

Overview of this book

Getting clean data to reveal insights is essential, as directly jumping into data analysis without proper data cleaning may lead to incorrect results. This book shows you tools and techniques that you can apply to clean and handle data with Python. You'll begin by getting familiar with the shape of data by using practices that can be deployed routinely with most data sources. Then, the book teaches you how to manipulate data to get it into a useful form. You'll also learn how to filter and summarize data to gain insights and better understand what makes sense and what does not, along with discovering how to operate on data to address the issues you've identified. Moving on, you'll perform key tasks, such as handling missing values, validating errors, removing duplicate data, monitoring high volumes of data, and handling outliers and invalid dates. Next, you'll cover recipes on using supervised learning and Naive Bayes analysis to identify unexpected values and classification errors, and generate visualizations for exploratory data analysis (EDA) to visualize unexpected values. Finally, you'll build functions and classes that you can reuse without modification when you have new data. By the end of this Python book, you'll be equipped with all the key skills that you need to clean data and diagnose problems within it.
Table of Contents (12 chapters)

Doing many-to-many merges

Many-to-many merges have duplicate merge-by values in both the left and right DataFrames. We should only rarely need to do a many-to-many merge. Even when data comes to us in that form, it is often because we are missing the central file in multiple one-to-many relationships. For example, there are donor, donor contributions, and donor contact information data tables, and the last two files contain multiple rows per donor. However, in this case, we do not have access to the donor file, which has a one-to-many relationship with both the contributions and contact information files. This happens more frequently than you may think. People sometimes give us data with little awareness of the underlying structure. When I do a many-to-many merge, it is typically because I am missing some key information rather than because that was how the database was designed.

Many-to-many merges return the Cartesian product of the merge-by column values. So, if a donor ID appears...