aes: Construct aesthetic mappings

In SahaRahul/ggplot2: Create Elegant Data Visualisations Using the Grammar of Graphics

Description

Aesthetic mappings describe how variables in the data are mapped to visual properties (aesthetics) of geoms. Aesthetic mappings can be set in ggplot2() and in individual layers.

Usage

aes(x, y, ...)

Arguments

x, y, ...

List of name value pairs giving aesthetics to map to variables. The names for x and y aesthetics are typically omitted because they are so common; all other aesthetics must be named.

Details

This function also standardise aesthetic names by performing partial matching, converting color to colour, and translating old style R names to ggplot names (eg. pch to shape, cex to size).

Quasiquotation

aes() is a quoting function. This means that its inputs are quoted to be evaluated in the context of the data. This makes it easy to work with variables from the data frame because you can name those directly. The flip side is that you have to use quasiquotation to program with aes(). See a tidy evaluation tutorial such as the dplyr programming vignette to learn more about these techniques.

See Also

vars() for another quoting function designed for faceting specifications.

Examples

aes(x = mpg, y = wt)
aes(mpg, wt)

# You can also map aesthetics to functions of variables
aes(x = mpg ^ 2, y = wt / cyl)

# Aesthetic names are automatically standardised
aes(col = x)
aes(fg = x)
aes(color = x)
aes(colour = x)

# aes is almost always used with ggplot() or a layer
ggplot(mpg, aes(displ, hwy)) + geom_point()
ggplot(mpg) + geom_point(aes(displ, hwy))

# Aesthetics supplied to ggplot() are used as defaults for every layer
# you can override them, or supply different aesthetics for each layer


# aes() is a quoting function, so you need to use tidy evaluation
# techniques to create wrappers around ggplot2 pipelines. The
# simplest case occurs when your wrapper takes dots:
scatter_by <- function(data, ...) {
  ggplot(data) + geom_point(aes(...))
}
scatter_by(mtcars, disp, drat)

# If your wrapper has a more specific interface with named arguments,
# you need to use the "enquote and unquote" technique:
scatter_by <- function(data, x, y) {
  ggplot(data) + geom_point(aes(!!enquo(x), !!enquo(y)))
}
scatter_by(mtcars, disp, drat)

# Note that users of your wrapper can use their own functions in the
# quoted expressions and all will resolve as it should!
cut3 <- function(x) cut_number(x, 3)
scatter_by(mtcars, cut3(disp), drat)

SahaRahul/ggplot2 documentation built on May 17, 2019, 1:46 p.m.