Book Image

The Data Wrangling Workshop - Second Edition

By : Brian Lipp, Shubhadeep Roychowdhury, Dr. Tirthajyoti Sarkar
Book Image

The Data Wrangling Workshop - Second Edition

By: Brian Lipp, Shubhadeep Roychowdhury, Dr. Tirthajyoti Sarkar

Overview of this book

While a huge amount of data is readily available to us, it is not useful in its raw form. For data to be meaningful, it must be curated and refined. If you’re a beginner, then The Data Wrangling Workshop will help to break down the process for you. You’ll start with the basics and build your knowledge, progressing from the core aspects behind data wrangling, to using the most popular tools and techniques. This book starts by showing you how to work with data structures using Python. Through examples and activities, you’ll understand why you should stay away from traditional methods of data cleaning used in other languages and take advantage of the specialized pre-built routines in Python. Later, you’ll learn how to use the same Python backend to extract and transform data from an array of sources, including the internet, large database vaults, and Excel financial tables. To help you prepare for more challenging scenarios, the book teaches you how to handle missing or incorrect data, and reformat it based on the requirements from your downstream analytics tool. By the end of this book, you will have developed a solid understanding of how to perform data wrangling with Python, and learned several techniques and best practices to extract, clean, transform, and format your data efficiently, from a diverse array of sources.
Table of Contents (11 chapters)


Now, we will learn how to exploit the relationship we just built. This means that if we have the primary key from one table, we can recover all the data needed from that table and also all the linked rows from the child table. To achieve this, we will use something called a join.

A join is basically a way to retrieve linked rows from two tables using any kind of primary key – foreign key relation that they have. There are many types of join, including INNER, LEFT OUTER, RIGHT OUTER, FULL OUTER, and CROSS. They are used in different situations. However, most of the time, in simple 1: N relations, we end up using an INNER join. In Chapter 1, Introduction to Data Wrangling with Python, we learned about sets. We can view an INNER join as an intersection of two sets. The following diagram illustrate the concepts:

Figure 8.7: A diagram representing the intersection join

Here, A represents one table, and B represents another. The meaning of having...