The polar coordinate system is most commonly used for pie charts, which are a stacked bar chart in polar coordinates. coord_radial() has extended options.

## Usage

coord_polar(theta = "x", start = 0, direction = 1, clip = "on")

theta = "x",
start = 0,
end = NULL,
expand = TRUE,
direction = 1,
clip = "off",
r.axis.inside = NULL,
rotate.angle = FALSE,
r_axis_inside = deprecated(),
rotate_angle = deprecated()
)

## Arguments

theta

variable to map angle to (x or y)

start

Offset of starting point from 12 o'clock in radians. Offset is applied clockwise or anticlockwise depending on value of direction.

direction

1, clockwise; -1, anticlockwise

clip

Should drawing be clipped to the extent of the plot panel? A setting of "on" (the default) means yes, and a setting of "off" means no. For details, please see coord_cartesian().

end

Position from 12 o'clock in radians where plot ends, to allow for partial polar coordinates. The default, NULL, is set to start + 2 * pi.

expand

If TRUE, the default, adds a small expansion factor the the limits to prevent overlap between data and axes. If FALSE, limits are taken directly from the scale.

r.axis.inside

If TRUE, places the radius axis inside the panel. If FALSE, places the radius axis next to the panel. The default, NULL, places the radius axis outside if the start and end arguments form a full circle.

rotate.angle

If TRUE, transforms the angle aesthetic in data in accordance with the computed theta position. If FALSE (default), no such transformation is performed. Can be useful to rotate text geoms in alignment with the coordinates.

A numeric between 0 and 1 setting the size of a inner.radius hole.

r_axis_inside, rotate_angle

## Note

In coord_radial(), position guides are can be defined by using guides(r = ..., theta = ..., r.sec = ..., theta.sec = ...). Note that these guides require r and theta as available aesthetics. The classic guide_axis() can be used for the r positions and guide_axis_theta() can be used for the theta positions. Using the theta.sec position is only sensible when inner.radius > 0.

The polar coordinates section of the online ggplot2 book.

## Examples

# NOTE: Use these plots with caution - polar coordinates has
# major perceptual problems.  The main point of these examples is
# to demonstrate how these common plots can be described in the
# grammar.  Use with EXTREME caution.

#' # A pie chart = stacked bar chart + polar coordinates
pie <- ggplot(mtcars, aes(x = factor(1), fill = factor(cyl))) +
geom_bar(width = 1)
pie + coord_polar(theta = "y")

# \donttest{

# A coxcomb plot = bar chart + polar coordinates
cxc <- ggplot(mtcars, aes(x = factor(cyl))) +
geom_bar(width = 1, colour = "black")
cxc + coord_polar()

# A new type of plot?
cxc + coord_polar(theta = "y")

# The bullseye chart
pie + coord_polar()

# Hadley's favourite pie chart
df <- data.frame(
variable = c("does not resemble", "resembles"),
value = c(20, 80)
)
ggplot(df, aes(x = "", y = value, fill = variable)) +
geom_col(width = 1) +
scale_fill_manual(values = c("red", "yellow")) +
coord_polar("y", start = pi / 3) +
labs(title = "Pac man")

# Windrose + doughnut plot
if (require("ggplot2movies")) {
movies$rrating <- cut_interval(movies$rating, length = 1)
movies$budgetq <- cut_number(movies$budget, 4)

doh <- ggplot(movies, aes(x = rrating, fill = budgetq))

# Wind rose
doh + geom_bar(width = 1) + coord_polar()
# Race track plot
doh + geom_bar(width = 0.9, position = "fill") + coord_polar(theta = "y")
}