Rug plots: geom_rug

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

alias Giggly.Plot

mtcars = Giggly.Datasets.mtcars()

render = fn plot ->
  plot
  |> Giggly.to_svg()
  |> IO.iodata_to_binary()
  |> Kino.Image.new(:svg)
end

About this notebook

This notebook follows the examples on ggplot2's reference page for geom_rug(), 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.

A rug plot adds the two one-dimensional distributions to a two-dimensional display, such as a scatter plot: a short line at the edge of the panel for each row's x, and another for its y. It draws every row, so it suits small tables. Giggly has no rugs yet, but Giggly.Plot.geom_point/3 draws the scatter plot they are added to. A plot is described with Giggly.Plot and drawn with Giggly.to_svg/2, which returns an SVG document. The setup cell aliases Giggly.Plot, so the cells write Plot.new/2, and defines render, which draws a plot and shows it below the cell with Kino.Image. The cells draw Giggly.Datasets.mtcars/0, R's mtcars: 32 cars from the 1974 Motor Trend US magazine, which the setup cell binds to mtcars, R's name for it.

A scatter plot

p <- ggplot(mtcars, aes(wt, mpg)) +
  geom_point()
p

mtcars
|> Plot.new(%{x: :wt, y: :mpg})
|> Plot.geom_point()
|> render.()

Rugs along the sides

p + geom_rug()
p + geom_rug(sides="b")    # Rug on bottom only
p + geom_rug(sides="trbl") # All four sides

By default the rug runs along the bottom and the left, sides = "bl".

Not in Giggly yet: geom_rug() and its sides option.

Jittering the rug

# Use jittering to avoid overplotting for smaller datasets
ggplot(mpg, aes(displ, cty)) +
  geom_point() +
  geom_rug()

ggplot(mpg, aes(displ, cty)) +
  geom_jitter() +
  geom_rug(alpha = 1/2, position = "jitter")

displ and cty take few distinct values, so many cars share a point and a rug line. Jittering moves each by a small random amount, so they can be told apart.

Not in Giggly yet: geom_rug(), geom_jitter() and position_jitter().

Rugs outside the panel

# move the rug tassels to outside the plot
# remember to set clip = "off".
p +
  geom_rug(outside = TRUE) +
  coord_cartesian(clip = "off")

Not in Giggly yet: geom_rug() and its outside option, and coord_cartesian()'s clip option.

Rugs on the top and right

# set sides to top right, and then move the margins
p +
  geom_rug(outside = TRUE, sides = "tr") +
  coord_cartesian(clip = "off") +
  theme(plot.margin = margin_auto(1, unit = "cm"))

Not in Giggly yet: geom_rug() and its outside and sides options, and coord_cartesian()'s clip option.

Longer rug lines

# increase the line length and
# expand axis to avoid overplotting
p +
  geom_rug(length = unit(0.05, "npc")) +
  scale_y_continuous(expand = c(0.1, 0.1))

Not in Giggly yet: geom_rug() and its length option.