1 Introduction

Tidyverse grammars like dplyr have a distinctive look and feel. This is in part because their design follows a set of principles. Their most important feature is that they let you work with your data as if they were actual objects in your workspace. In a way, the data frame temporarily becomes the workspace.

Data masking makes it easy and natural to read and write data manipulation code, but it has a flip side. It is easier to refer to objects in the mask when you know their names in advance, but it is harder when the names are unknown at the time of writing. In particular, it is harder to make indirect references with column names stored in variables or passed as function arguments.

Tidy evaluation is a set of concepts and tools that make it possible to use tidyverse grammars when columns are specified indirectly. In particular, you will need to learn some tidy eval to extract a tidyverse pipeline in a reusable function.

The first chapter Why and how provides the motivation for tidy eval, presents the problems that it poses in day-to-day programming, and the general theory and tools for solving those. If you are in a hurry, you can jump straight to Do you need tidy eval?. A lot can be done without writing a single line of tidy eval! If you are positive you need it to solve your problem, Getting up to speed is a self-contained chapter that will teach you the basic workflow of wrapping a tidyverse pipeline in a reusable function. The book ends with a series of recipes and idioms for solving various dplyr and ggplot2 problems.