Book Image

Learning Spark SQL

By : Aurobindo Sarkar
Book Image

Learning Spark SQL

By: Aurobindo Sarkar

Overview of this book

In the past year, Apache Spark has been increasingly adopted for the development of distributed applications. Spark SQL APIs provide an optimized interface that helps developers build such applications quickly and easily. However, designing web-scale production applications using Spark SQL APIs can be a complex task. Hence, understanding the design and implementation best practices before you start your project will help you avoid these problems. This book gives an insight into the engineering practices used to design and build real-world, Spark-based applications. The book's hands-on examples will give you the required confidence to work on any future projects you encounter in Spark SQL. It starts by familiarizing you with data exploration and data munging tasks using Spark SQL and Scala. Extensive code examples will help you understand the methods used to implement typical use-cases for various types of applications. You will get a walkthrough of the key concepts and terms that are common to streaming, machine learning, and graph applications. You will also learn key performance-tuning details including Cost Based Optimization (Spark 2.2) in Spark SQL applications. Finally, you will move on to learning how such systems are architected and deployed for a successful delivery of your project.
Table of Contents (19 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Munging textual data


In this section, we explore data munging techniques for typical analysis situations. Many text-based analyses tasks require computing word counts, removing stop words, stemming, and so on. In addition, we will also explore how you can process multiple files, one at a time, from HDFS directories.

First, we import all the classes that will be used in this section:

Processing multiple input data files

In the next few steps, we initialize a set of variables for defining the directory containing the input files, and an empty RDD. We also create a list of filenames the input HDFS directory. In the following example, we will work with files contained in a single directory; however, the techniques can easily be extended across all 20 newsgroup sub-directories.

Next, we write a function to compute the word counts for each file and collect the results in an ArrayBuffer:

We have included a print statement to display the file names as they are picked up for processing, as follows:

We...