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 one-to-one merges

The remainder of this chapter will explore combining data horizontally; that is, merging columns from a data table with columns from another data table. Borrowing from SQL development, we typically talk about such operations as join operations: left joins, right joins, inner joins, and outer joins. This recipe examines one-to-one merges, where the merge-by values are unduplicated in both files. Subsequent recipes will demonstrate one-to-many merges, where the merge-by values are duplicated on the right data table; and many-to-many merges, where merge-by values are duplicated on both the left and right data tables.

We often speak of left and right sides of a merge, a convention that we will follow throughout this chapter. But this is of no real consequence, other than for clarity of exposition. We can accomplish exactly the same thing with a merge if A were the left data table and B were the right data table and vice versa.

I am using the expressions merge...