Book Image

Large Scale Machine Learning with Python

By : Bastiaan Sjardin, Alberto Boschetti
Book Image

Large Scale Machine Learning with Python

By: Bastiaan Sjardin, Alberto Boschetti

Overview of this book

Large Python machine learning projects involve new problems associated with specialized machine learning architectures and designs that many data scientists have yet to tackle. But finding algorithms and designing and building platforms that deal with large sets of data is a growing need. Data scientists have to manage and maintain increasingly complex data projects, and with the rise of big data comes an increasing demand for computational and algorithmic efficiency. Large Scale Machine Learning with Python uncovers a new wave of machine learning algorithms that meet scalability demands together with a high predictive accuracy. Dive into scalable machine learning and the three forms of scalability. Speed up algorithms that can be used on a desktop computer with tips on parallelization and memory allocation. Get to grips with new algorithms that are specifically designed for large projects and can handle bigger files, and learn about machine learning in big data environments. We will also cover the most effective machine learning techniques on a map reduce framework in Hadoop and Spark in Python.
Table of Contents (17 chapters)
Large Scale Machine Learning with Python
Credits
About the Authors
About the Reviewer
www.PacktPub.com
Preface
Index

Data preprocessing in Spark


So far, we've seen how to load text data from the local filesystem and HDFS. Text files can contain either unstructured data (like a text document) or structured data (like a CSV file). As for semi-structured data, just like files containing JSON objects, Spark has special routines able to transform a file into a DataFrame, similar to the DataFrame in R and Python pandas. DataFrames are very similar to RDBMS tables, where a schema is set.

JSON files and Spark DataFrames

In order to import JSON-compliant files, we should first create a SQL context, creating a SQLContext object from the local Spark Context:

In:from pyspark.sql import SQLContext
sqlContext = SQLContext(sc)

Now, let's see the content of a small JSON file (it's provided in the Vagrant virtual machine). It's a JSON representation of a table with six rows and three columns, where some attributes are missing (such as the gender attribute for the user with user_id=0):

In:!cat /home/vagrant/datasets/users.json...