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

The key concepts of k-means and DBSCAN clustering

With k-means clustering, we identify k clusters, each with a center, or centroid. The centroid is the point that minimizes the total squared distance between it and the other data points in the cluster.

An example with made-up data should help here. The data points in Figure 16.1 seem to be in three clusters. (It is not usually that easy to visualize the number of clusters, k.)

Figure 16.1 – Data points with three discernible clusters

We perform the following steps to construct the clusters:

  1. Assign a random point as the center of each cluster.
  2. Calculate the distance of each point from the center of each cluster.
  3. Assign data points to a cluster based on their proximity to the center point. These first three steps are illustrated in Figure 16.2. The points with an X are the randomly chosen cluster centers (with k set at 3). Data points that are closer to the cluster center point than...