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Statistics for Machine Learning

You're reading from  Statistics for Machine Learning

Product type Book
Published in Jul 2017
Publisher Packt
ISBN-13 9781788295758
Pages 442 pages
Edition 1st Edition
Languages
Concepts
Author (1):
Pratap Dangeti Pratap Dangeti
Profile icon Pratap Dangeti

Table of Contents (16) Chapters

Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
1. Journey from Statistics to Machine Learning 2. Parallelism of Statistics and Machine Learning 3. Logistic Regression Versus Random Forest 4. Tree-Based Machine Learning Models 5. K-Nearest Neighbors and Naive Bayes 6. Support Vector Machines and Neural Networks 7. Recommendation Engines 8. Unsupervised Learning 9. Reinforcement Learning

Laplace estimator


In the previous calculation, all the values are nonzeros, which makes calculations well. Whereas in practice some words never appear in past for specific category and suddenly appear at later stages, which makes entire calculations as zeros.

For example, in the previous equation W3 did have a 0 value instead of 13, and it will convert entire equations to 0 altogether:

In order to avoid this situation, Laplace estimator essentially adds a small number to each of the counts in the frequency table, which ensures that each feature has a nonzero probability of occurring with each class. Usually Laplace estimator is set to 1, which ensures that each class-feature combination is found in the data at least once:

Note

If you observe the equation carefully, value 1 is added to all three words in numerator and at the same time three has been added to all denominators to provide equivalence.

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