Book Image

Practical Data Wrangling

By : Allan Visochek
Book Image

Practical Data Wrangling

By: Allan Visochek

Overview of this book

Around 80% of time in data analysis is spent on cleaning and preparing data for analysis. This is, however, an important task, and is a prerequisite to the rest of the data analysis workflow, including visualization, analysis and reporting. Python and R are considered a popular choice of tool for data analysis, and have packages that can be best used to manipulate different kinds of data, as per your requirements. This book will show you the different data wrangling techniques, and how you can leverage the power of Python and R packages to implement them. You’ll start by understanding the data wrangling process and get a solid foundation to work with different types of data. You’ll work with different data structures and acquire and parse data from various locations. You’ll also see how to reshape the layout of data and manipulate, summarize, and join data sets. Finally, we conclude with a quick primer on accessing and processing data from databases, conducting data exploration, and storing and retrieving data quickly using databases. The book includes practical examples on each of these points using simple and real-world data sets to give you an easier understanding. By the end of the book, you’ll have a thorough understanding of all the data wrangling concepts and how to implement them in the best possible way.
Table of Contents (16 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Filtering the rows of a dataframe


You can filter rows as a function of the content of a row using the filter() function. (Recall from the previous chapters that you used filtering steps to remove outliers and NA values.)

In the filter() function, each of the arguments following the first is what the documentation refers to as a logical predicate. In other words, each of the arguments are assertions that some logical expression should be true.

The logical expressions used for filtering are defined in terms of the column names of the input dataframe.  Here are some possible examples of logical predicates that could be used as arguments to the filter() function:

  • column.name > 6
  • column.name == "abc"
  • !is.na( column.name )

A good application of the filter() function to the fuel economy dataset could be to find data for just one model. There is likely a lot of variation in the fuel economy data from model to model, so we could get a more consistent result by just focusing on one model.

In the following...