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

Feature scaling

Often, the features we want to use in our model are on very different scales. Put simply, the distance between the minimum and maximum values, or the range, varies substantially across possible features. For example, in the COVID-19 data, the total cases feature goes from 1 to almost 34 million, while aged 65 or older goes from 9 to 27 (the number represents the percentage of the population).

Having features on very different scales impacts many machine learning algorithms. For example, KNN models often use Euclidean distance, and features with greater ranges will have a greater influence on the model. Scaling can address this problem.

In this section, we will go over two popular approaches to scaling: min-max scaling and standard (or z-score) scaling. Min-max scaling replaces each value with its location in the range. More precisely, the following happens:

=

Here, is the min-max score, is the value for the observation of the feature, and and are...