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Learning PySpark

You're reading from   Learning PySpark Build data-intensive applications locally and deploy at scale using the combined powers of Python and Spark 2.0

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Product type Paperback
Published in Feb 2017
Publisher Packt
ISBN-13 9781786463708
Length 274 pages
Edition 1st Edition
Languages
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Authors (2):
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Denny Lee Denny Lee
Author Profile Icon Denny Lee
Denny Lee
Tomasz Drabas Tomasz Drabas
Author Profile Icon Tomasz Drabas
Tomasz Drabas
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Toc

Table of Contents (13) Chapters Close

Preface 1. Understanding Spark 2. Resilient Distributed Datasets FREE CHAPTER 3. DataFrames 4. Prepare Data for Modeling 5. Introducing MLlib 6. Introducing the ML Package 7. GraphFrames 8. TensorFrames 9. Polyglot Persistence with Blaze 10. Structured Streaming 11. Packaging Spark Applications Index

Getting to know your data


In order to build a statistical model in an informed way, an intimate knowledge of the dataset is necessary. Without knowing the data it is possible to build a successful model, but it is then a much more arduous task, or it would require more technical resources to test all the possible combinations of features. Therefore, after spending the required 80% of the time cleaning the data, we spend the next 15% getting to know it!

Descriptive statistics

I normally start with descriptive statistics. Even though the DataFrames expose the .describe() method, since we are working with MLlib, we will use the .colStats(...) method.

Note

A word of warning: the .colStats(...) calculates the descriptive statistics based on a sample. For real world datasets this should not really matter but if your dataset has less than 100 observations you might get some strange results.

The method takes an RDD of data to calculate the descriptive statistics of and return a MultivariateStatisticalSummary...

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