Adding to a plot: gg-add

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

alias Giggly.Plot

mpg = Giggly.Datasets.mpg()

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 add_gg(), which covers %+% 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 ggplot2, + adds a component to a plot: a layer, a scale, a theme, a coordinate system, a facet, or a mapping that replaces the plot's own. Adding a list adds each of its elements in turn, and replacing the plot's data takes %+%. A Giggly plot is built with a pipe instead: each function in Giggly.Plot takes a plot and returns it with a layer added, as Giggly.Plot.geom_point/3 does, or with its facet or coordinate system replaced, as Giggly.Plot.facet_wrap/3 and Giggly.Plot.coord_radial/1 do. The data is given once, to Giggly.Plot.new/2. A plot is 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. It binds Giggly.Datasets.mpg/0, ggplot2's mpg, to mpg, ggplot2's name for it.

Adding a layer

base <-
 ggplot(mpg, aes(displ, hwy)) +
 geom_point()
base + geom_smooth()

mpg has fewer than 1,000 rows, so the smooth is a loess fit. Giggly fits a loess curve at each of its points directly, as R's loess(surface = "direct") does, where R's default joins fits made at fewer places, so its curve sits up to 1.7 points from R's here, and its band's edges up to 2.9.

base =
  mpg
  |> Plot.new(%{x: :displ, y: :hwy})
  |> Plot.geom_point()

base
|> Plot.geom_smooth()
|> render.()

Replacing the data

# To override the data, you must use %+%
base %+% subset(mpg, fl == "p")

R's subset() keeps the cars that take premium fuel, fl == "p", and %+% makes them the plot's data. Not in Giggly yet: %+%, replacing a plot's data.

Adding a list

# Alternatively, you can add multiple components with a list.
# This can be useful to return from a function.
base + list(subset(mpg, fl == "p"), geom_smooth())

A data frame in the list replaces the plot's data, as %+% does. Not in Giggly yet: replacing a plot's data. Giggly adds components with a pipe rather than a list, so a function that pipes a plot through several of them returns it with all of them added.