GGPlot AES: How to Assign Aesthetics in GGPlot2

Prerequisites

Load required packages and set the theme function theme_bw() as the default theme:

library(ggplot2) 
theme_set(theme_bw())

Basics

Map aesthetics to variables and to functions of variables:

# Map aesthetics to variables
ggplot(ToothGrowth, aes(x = supp, y = len)) +
  geom_boxplot()

# Map aesthetics to functions of variables
ggplot(mtcars, aes(x = mpg ^ 2, y = wt / cyl)) +
  geom_point()

Aesthetics can be also mapped to constants:

# map x to constant: 1
ggplot(ToothGrowth, aes(x = factor(1), y = len)) +
  geom_boxplot(width = 0.5) +
  geom_jitter(width = 0.1)

For example:

# Use this 
ggplot(mpg, aes(displ, hwy)) + geom_point()

# or this
ggplot(mpg) + geom_point(aes(displ, hwy))

Color and fill

# Color
ggplot(ToothGrowth, aes(supp, len)) +
  geom_boxplot(aes(color = supp))

# Fill
ggplot(ToothGrowth, aes(supp, len)) +
  geom_boxplot(aes(fill = supp))

Shape

Change point shapes by groups:

ggplot(iris, aes(Sepal.Length, Sepal.Width)) +
  geom_point(aes(shape = Species))

Group and line type

In line plot, for example, group aesthetic is used to ensure lines are drawn separately for each group

# Data
df2 <- data.frame(supp=rep(c("VC", "OJ"), each=3),
                dose=rep(c("D0.5", "D1", "D2"),2),
                len=c(6.8, 15, 33, 4.2, 10, 29.5))

head(df2, 4)

##   supp dose  len
## 1   VC D0.5  6.8
## 2   VC   D1 15.0
## 3   VC   D2 33.0
## 4   OJ D0.5  4.2

# Create a grouped line plot
ggplot(df2, aes(dose, len, group = supp)) +
  geom_line() +
  geom_point()


# Change linetype by groups
ggplot(df2, aes(dose, len, group = supp)) +
  geom_line(aes(linetype = supp)) +
  geom_point()

Label

ggplot(df2, aes(dose, len, group = supp)) +
  geom_line() +
  geom_point() +
  geom_text(aes(label = len, vjust = -0.5))

Create wrappers around ggplot2 pipelines

aes() automatically quotes all its arguments, so you need to use tidy-evaluation to create wrappers around ggplot2 pipelines.

1. Simplest case: your wrapper takes dots

scatter_plot <- function(data, ...) {
  ggplot(data) + geom_point(aes(...))
}
scatter_plot(mtcars, disp, drat)

2. Your wrapper has named arguments. You need “enquote and unquote”

scatter_plot <- function(data, x, y) {
  x <- enquo(x)
  y <- enquo(y)

  ggplot(data) + geom_point(aes(!!x, !!y))
}
scatter_plot(mtcars, disp, drat)

cut3 <- function(x) cut_number(x, 3)
scatter_plot(mtcars, cut3(disp), drat)