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 with medium or high cardinality

When we are working with a categorical feature that has many unique values, say 10 or more, it can be impractical to create a dummy variable for each value. When there is high cardinality, that is, a very large number of unique values, there might be too few observations with certain values to provide much information for our models. At the extreme, with an ID variable, there is just one observation for each value.

There are a couple of ways in which to handle medium or high cardinality. One way is to create dummies for the top k categories and group the remaining values into an other category. Another way is to use feature hashing, also known as the hashing trick. In this section, we will explore both strategies. We will be using the COVID-19 dataset for this example:

  1. Let's create training and testing DataFrames from COVID-19 data, and import the feature_engine and category_encoders libraries:
    import pandas...