Polar coordinates: coord_radial

Mix.install([
  {:giggly, path: Path.join(__DIR__, "..")},
  {:kino, "~> 0.19"}
  ])

About this notebook

This notebook follows the examples on ggplot2's reference page for coord_radial(), which covers coord_polar() too, in the order the page gives them. Each example shows ggplot2's code first and then Giggly's. An example Giggly cannot draw yet keeps its ggplot2 code and names what it is waiting for, so the page is also a list of what remains.

In polar coordinates one position becomes an angle around a centre and the other a distance from it; a pie chart is a stacked bar chart drawn this way. coord_polar() is superseded by coord_radial(), whose options choose which of x and y is the angle (theta), where the circle starts and ends, the limits of the angle and the radius, whether the scales expand, the size of a hole in the middle, and where the radius axis goes. Giggly.Plot.coord_radial/1 is ggplot2's coord_radial() without options, so it draws as coord_radial() does with every option at its default. Giggly has no coord_polar() yet, and draws no bars in radial coordinates: a bar layer under Giggly.Plot.coord_radial/1 raises.

A pie chart

# 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_radial(theta = "y", expand = FALSE)

Not in Giggly yet: bars in radial coordinates, and coord_radial()'s theta and expand options.

A coxcomb plot

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

Not in Giggly yet: bars in radial coordinates, and coord_radial()'s expand option.

Counts as angles

# A new type of plot?
cxc + coord_radial(theta = "y", expand = FALSE)

Not in Giggly yet: bars in radial coordinates, and coord_radial()'s theta and expand options.

A bullseye chart

# The bullseye chart
pie + coord_radial(expand = FALSE)

Not in Giggly yet: bars in radial coordinates, and coord_radial()'s expand option.

A pie chart's colours and starting angle

# 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_radial("y", start = pi / 3, expand =  FALSE) +
  labs(title = "Pac man")

Not in Giggly yet: bars in radial coordinates, and coord_radial()'s theta, start and expand options.

A wind rose and a race track

R's if (require("ggplot2movies")) runs the example only when the ggplot2movies package, which holds the movies dataset, is installed.

# 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_radial(expand = FALSE)
# Race track plot
doh + geom_bar(width = 0.9, position = "fill") +
  coord_radial(theta = "y", expand = FALSE)
}

Not in Giggly yet: the movies dataset, cut_interval() and cut_number(), bars in radial coordinates, position_fill(), and coord_radial()'s theta and expand options.

A partial circle

# A partial polar plot
ggplot(mtcars, aes(disp, mpg)) +
  geom_point() +
  coord_radial(start = -0.4 * pi, end = 0.4 * pi, inner.radius = 0.3)

Not in Giggly yet: coord_radial()'s start, end and inner.radius options.

Limits

# Similar with coord_cartesian(), you can set limits.
ggplot(mtcars, aes(disp, mpg)) +
  geom_point() +
  coord_radial(
    start = -0.4 * pi,
    end = 0.4 * pi, inner.radius = 0.3,
    thetalim = c(200, 300),
    rlim = c(15, 30),
  )

Not in Giggly yet: coord_radial()'s start, end, inner.radius, thetalim and rlim options.