Mean or median imputation consists of replacing missing values with the variable mean or median. This can only be performed in numerical variables. The mean or the median is calculated using a train set, and these values are used to impute missing data in train and test sets, as well as in future data we intend to score with the machine learning model. Therefore, we need to store these mean and median values. Scikit-learn and Feature-engine transformers learn the parameters from the train set and store these parameters for future use. So, in this recipe, we will learn how to perform mean or median imputation using the scikit-learn and Feature-engine libraries and pandas for comparison.

Python Feature Engineering Cookbook
By :

Python Feature Engineering Cookbook
By:
Overview of this book
Feature engineering is invaluable for developing and enriching your machine learning models. In this cookbook, you will work with the best tools to streamline your feature engineering pipelines and techniques and simplify and improve the quality of your code.
Using Python libraries such as pandas, scikit-learn, Featuretools, and Feature-engine, you’ll learn how to work with both continuous and discrete datasets and be able to transform features from unstructured datasets. You will develop the skills necessary to select the best features as well as the most suitable extraction techniques. This book will cover Python recipes that will help you automate feature engineering to simplify complex processes. You’ll also get to grips with different feature engineering strategies, such as the box-cox transform, power transform, and log transform across machine learning, reinforcement learning, and natural language processing (NLP) domains.
By the end of this book, you’ll have discovered tips and practical solutions to all of your feature engineering problems.
Table of Contents (13 chapters)
Preface
Foreseeing Variable Problems When Building ML Models
Imputing Missing Data
Encoding Categorical Variables
Transforming Numerical Variables
Performing Variable Discretization
Working with Outliers
Deriving Features from Dates and Time Variables
Performing Feature Scaling
Applying Mathematical Computations to Features
Creating Features with Transactional and Time Series Data
Extracting Features from Text Variables
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