Book Image

Scala for Data Science

By : Pascal Bugnion
Book Image

Scala for Data Science

By: Pascal Bugnion

Overview of this book

Scala is a multi-paradigm programming language (it supports both object-oriented and functional programming) and scripting language used to build applications for the JVM. Languages such as R, Python, Java, and so on are mostly used for data science. It is particularly good at analyzing large sets of data without any significant impact on performance and thus Scala is being adopted by many developers and data scientists. Data scientists might be aware that building applications that are truly scalable is hard. Scala, with its powerful functional libraries for interacting with databases and building scalable frameworks will give you the tools to construct robust data pipelines. This book will introduce you to the libraries for ingesting, storing, manipulating, processing, and visualizing data in Scala. Packed with real-world examples and interesting data sets, this book will teach you to ingest data from flat files and web APIs and store it in a SQL or NoSQL database. It will show you how to design scalable architectures to process and modelling your data, starting from simple concurrency constructs such as parallel collections and futures, through to actor systems and Apache Spark. As well as Scala’s emphasis on functional structures and immutability, you will learn how to use the right parallel construct for the job at hand, minimizing development time without compromising scalability. Finally, you will learn how to build beautiful interactive visualizations using web frameworks. This book gives tutorials on some of the most common Scala libraries for data science, allowing you to quickly get up to speed with building data science and data engineering solutions.
Table of Contents (22 chapters)
Scala for Data Science
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

SQL statements on DataFrames


By now, you will have noticed that many operations on DataFrames are inspired by SQL operations. Additionally, Spark allows us to register DataFrames as tables and query them with SQL statements directly. We can therefore build a temporary database as part of the program flow.

Let's register readingsDF as a temporary table:

scala> readingsDF.registerTempTable("readings")

This registers a temporary table that can be used in SQL queries. Registering a temporary table relies on the presence of a SQL context. The temporary tables are destroyed when the SQL context is destroyed (when we close the shell, for instance).

Let's explore what we can do with our temporary tables and the SQL context. We can first get a list of all the tables currently registered with the context:

scala> sqlContext.tables
DataFrame = [tableName: string, isTemporary: boolean]

This returns a DataFrame. In general, all operations on a SQL context that return data return DataFrames:

scala...