Nudged positions: position_nudge

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

alias Giggly.Plot

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 position_nudge(), 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.

position_nudge() moves every item a fixed distance along x, y or both, which is most useful for shifting items on a discrete scale by a small amount. Labels are the usual case, so geom_text() builds it in, as its nudge_x and nudge_y options; the distances can also be mapped, as the nudge_x and nudge_y aesthetics, to move each item its own way. Giggly nudges text, by Giggly.Plot.geom_text/3's nudge_x: and nudge_y: options; it has no position_nudge(), and maps no nudge_x or nudge_y. 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 examples make a small table of their own, as ggplot2's do.

Labels on the points

df <- data.frame(
  x = c(1,3,2,5),
  y = c("a","c","d","c")
)

ggplot(df, aes(x, y)) +
  geom_point() +
  geom_text(aes(label = y))

Unnudged, each label is drawn over its point.

df = %{"x" => [1.0, 3.0, 2.0, 5.0], "y" => ["a", "c", "d", "c"]}

df
|> Plot.new(%{x: :x, y: :y})
|> Plot.geom_point()
|> Plot.geom_text(%{label: :y})
|> render.()

Nudging the labels down

ggplot(df, aes(x, y)) +
  geom_point() +
  geom_text(aes(label = y), position = position_nudge(y = -0.1))

Not in Giggly yet: geom_text()'s position option and position_nudge(). Giggly nudges text by geom_text/3's own options, as the next example does.

Nudging in brief

# Or, in brief
ggplot(df, aes(x, y)) +
  geom_point() +
  geom_text(aes(label = y), nudge_y = -0.1)

y is discrete, its values a step apart, so each label moves down a tenth of that step.

df
|> Plot.new(%{x: :x, y: :y})
|> Plot.geom_point()
|> Plot.geom_text(%{label: :y}, nudge_y: -0.1)
|> render.()

Nudging each label its own way

# For each text individually
ggplot(df, aes(x, y)) +
  geom_point() +
  geom_text(aes(label = y, nudge_y = c(-0.1, 0.1, -0.1, 0.1)))

A vector in aes() gives one value per row, so the labels go down and up in turn.

Not in Giggly yet: mapping nudge_y, and a vector outside the data in a mapping, here c(-0.1, 0.1, -0.1, 0.1).