Book Image

Mastering Machine Learning with scikit-learn - Second Edition

By : Gavin Hackeling
Book Image

Mastering Machine Learning with scikit-learn - Second Edition

By: Gavin Hackeling

Overview of this book

Machine learning is the buzzword bringing computer science and statistics together to build smart and efficient models. Using powerful algorithms and techniques offered by machine learning you can automate any analytical model. This book examines a variety of machine learning models including popular machine learning algorithms such as k-nearest neighbors, logistic regression, naive Bayes, k-means, decision trees, and artificial neural networks. It discusses data preprocessing, hyperparameter optimization, and ensemble methods. You will build systems that classify documents, recognize images, detect ads, and more. You will learn to use scikit-learn’s API to extract features from categorical variables, text and images; evaluate model performance, and develop an intuition for how to improve your model’s performance. By the end of this book, you will master all required concepts of scikit-learn to build efficient models at work to carry out advanced tasks with the practical approach.
Table of Contents (22 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
9
From Decision Trees to Random Forests and Other Ensemble Methods
Index

Classification with KNN


Recall from Chapter 1, The Fundamentals of Machine Learning that the goal of classification tasks is to use one or more features to predict the value of a discrete response variable. Let's work through a toy classification problem. Assume that you must use a person's height and weight to predict his or her sex. This problem is called binary classification because the response variable can take one of two labels. The following table records nine training instances:

Height

Weight

Label

158 cm

64 kg

male

170 cm

66 kg

male

183 cm

84 kg

male

191 cm

80 kg

male

155 cm

49 kg

female

163 cm

59 kg

female

180 cm

67 kg

female

158 cm

54 kg

female

178 cm

77 kg

female

 

Unlike the previous chapter's simple linear regression problem, we are now using features from two explanatory variables to predict the value of the response variable. KNN is not limited to two features; the algorithm can use an arbitrary number of features, but more than three features cannot be visualized. Let's visualize the data by creating...