Book Image

Clojure Data Analysis Cookbook

By : Eric Rochester
Book Image

Clojure Data Analysis Cookbook

By: Eric Rochester

Overview of this book

<p>Data is everywhere and it's increasingly important to be able to gain insights that we can act on. Using Clojure for data analysis and collection, this book will show you how to gain fresh insights and perspectives from your data with an essential collection of practical, structured recipes.<br /><br />"The Clojure Data Analysis Cookbook" presents recipes for every stage of the data analysis process. Whether scraping data off a web page, performing data mining, or creating graphs for the web, this book has something for the task at hand.<br /><br />You'll learn how to acquire data, clean it up, and transform it into useful graphs which can then be analyzed and published to the Internet. Coverage includes advanced topics like processing data concurrently, applying powerful statistical techniques like Bayesian modelling, and even data mining algorithms such as K-means clustering, neural networks, and association rules.</p>
Table of Contents (18 chapters)
Clojure Data Analysis Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Managing program complexity with STM


The basis of Clojure's concurrency is its Software Transactional Memory (STM) system. Basically this extends the semantics of database transactions to the computer's memory.

The way the STM works is that we mark memory locations to be controlled by the STM using the ref function. We can then de-reference those anywhere using the deref function or the @ macro. But we can only change the values of a reference inside a dosync block. Then, when the point of execution gets to the end of a transaction, the STM performs a check. If any of the references that the transaction altered have been changed by another transaction, the transaction fails, and it's queued to be tried again. However, if none of the references have changed, then the transaction succeeds and is committed.

While we're in the transaction, to code outside it, those values don't appear to have changed. Once the transaction is committed, then any changes we make to those locations with ref-set...