Line widths: scale_linewidth

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

alias Giggly.Plot

economics = Giggly.Datasets.economics()

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 scale_linewidth(), which covers scale_linewidth_binned() 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.

scale_linewidth() maps a continuous column to the width of lines and of polygons' outlines, between a thinnest and a thickest width; scale_linewidth_binned() cuts the column into bins first. The size aesthetic can still set a line's width, for historical reasons, but linewidth keeps the width of a stroke apart from the size of an area. Giggly has Giggly.Plot.scale_linewidth_continuous/2 and Giggly.Plot.scale_linewidth_discrete/2, with their range:, but not ggplot2's short name, scale_linewidth(), nor binned line width scales (scale_linewidth_binned()), and by default maps linewidth to a column as ggplot2's default scale does, and draws the legend that reads it back. 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 data is Giggly.Datasets.economics/0, ggplot2's economics: US economic time series, one row a month from 1967 to 2015, which the setup cell binds to economics, ggplot2's name for it.

Line width from a column

p <- ggplot(economics, aes(date, unemploy, linewidth = uempmed)) +
  geom_line(lineend = "round")
p
p + scale_linewidth("Duration of\nunemployment")
p + scale_linewidth(range = c(0, 4))

uempmed is the median number of weeks unemployed. A scale's first argument titles its legend, and range sets the thinnest and the thickest widths. scale_linewidth() is Giggly.Plot.scale_linewidth_continuous/2, its title name:.

p =
  economics
  |> Plot.new(%{x: :date, y: :unemploy, linewidth: :uempmed})
  |> Plot.geom_line(lineend: :round)

render.(p)

p
|> Plot.scale_linewidth_continuous(name: "Duration of\nunemployment")
|> render.()

p
|> Plot.scale_linewidth_continuous(range: {0, 4})
|> render.()

Binned widths

# Binning can sometimes make it easier to match the scaled data to the legend
p + scale_linewidth_binned()

Not in Giggly yet: scale_linewidth_binned() and the legend that reads it back.