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

Using random forest for imputation

Random forest is an ensemble learning method. It uses bootstrap aggregating, also known as bagging, to improve model accuracy. It makes predictions by repeatedly taking the mean of multiple trees, yielding progressively better estimates. We will use the MissForest algorithm in this section, which is an application of the random forest algorithm to find missing value imputation.

MissForest starts by filling in the median or mode (for continuous or categorical features, respectively) for missing values, then uses random forest to predict values. Using this transformed dataset, with missing values replaced with initial predictions, MissForest generates new predictions, perhaps replacing the initial prediction with a better one. MissForest will typically go through at least four iterations of this process.

Running MissForest is even easier than using the KNN imputer, which we used in the previous section. We will impute values for the same wage...