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

Identifying missing values

Since identifying missing values is such an important part of an analyst's workflow, any tool we use needs to make it easy to regularly check for such values. Fortunately, pandas makes it quite simple to identify missing values.

We will be working with the National Longitudinal Survey (NLS) in this chapter. The NLS has one observation per survey respondent. Data for employment, earnings, and college enrollment for each year are stored in columns with suffixes representing the year, such as weeksworked16 and weeksworked17 for weeks worked in 2016 and 2017, respectively.

Note

We will also work with the COVID-19 data again. This dataset has one observation for each country that specifies the total COVID-19 cases and deaths, as well as some demographic data for each country.

Follow these steps to identify our missing values:

  1. Let's start by loading the NLS and COVID-19 data:
    import pandas as pd
    import numpy as np
    nls97 = pd.read_csv...