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

Key concepts of PCA

PCA produces multiple linear combinations of features and each linear combination is a component. It identifies a component that captures the largest amount of variance, and a second component that captures the largest amount of remaining variance, and then a third component, and so on until a stopping point we specify is reached. The stopping point can be based on the number of components, the percent of the variation explained, or domain knowledge.

One very useful characteristic of principal components is that they are mutually orthogonal. This means that they are uncorrelated, which is really good news for modeling. Figure 15.1 shows two components constructed from the features x1 and x2. The maximum variance is captured with PC1, the maximum remaining variance with PC2. (The data points in the figure are made up.) Notice that the two vectors are orthogonal (perpendicular).

Figure 15.1 – An illustration of PCA with two features...