Book Image

Data Cleaning and Exploration with Machine Learning

By : Michael Walker
Book Image

Data Cleaning and Exploration with Machine Learning

By: Michael Walker

Overview of this book

Many individuals who know how to run machine learning algorithms do not have a good sense of the statistical assumptions they make and how to match the properties of the data to the algorithm for the best results. As you start with this book, models are carefully chosen to help you grasp the underlying data, including in-feature importance and correlation, and the distribution of features and targets. The first two parts of the book introduce you to techniques for preparing data for ML algorithms, without being bashful about using some ML techniques for data cleaning, including anomaly detection and feature selection. The book then helps you apply that knowledge to a wide variety of ML tasks. You’ll gain an understanding of popular supervised and unsupervised algorithms, how to prepare data for them, and how to evaluate them. Next, you’ll build models and understand the relationships in your data, as well as perform cleaning and exploration tasks with that data. You’ll make quick progress in studying the distribution of variables, identifying anomalies, and examining bivariate relationships, as you focus more on the accuracy of predictions in this book. By the end of this book, you’ll be able to deal with complex data problems using unsupervised ML algorithms like principal component analysis and k-means clustering.
Table of Contents (23 chapters)
1
Section 1 – Data Cleaning and Machine Learning Algorithms
5
Section 2 – Preprocessing, Feature Selection, and Sampling
9
Section 3 – Modeling Continuous Targets with Supervised Learning
13
Section 4 – Modeling Dichotomous and Multiclass Targets with Supervised Learning
19
Section 5 – Clustering and Dimensionality Reduction with Unsupervised Learning

Encoding categorical features

There are several reasons why we might need to encode features before using them in most machine learning algorithms. First, these algorithms typically require numeric data. Second, when a categorical feature is represented with numbers, for example, 1 for female and 2 for male, we need to encode the values so that they are recognized as categorical. Third, the feature might actually be ordinal, with a discrete number of values that represent some meaningful ranking. Our models need to capture that ranking. Finally, a categorical feature might have a large number of values (known as high cardinality), and we might want our encoding to collapse categories.

We can handle the encoding of features with a limited number of values, say 15 or less, with one-hot encoding. In this section, we will, first, go over one-hot encoding and then discuss ordinal encoding. We will look at strategies for handling categorical features with high cardinality in the next...