Violin plots: geom_violin

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

About this notebook

This notebook follows the examples on ggplot2's reference page for geom_violin(), which covers stat_ydensity() 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.

A violin plot is a compact display of a continuous distribution, a blend of a box plot and a density plot: each group's density estimate, mirrored, drawn where a box plot would draw its box. stat_ydensity() computes the densities, and geom_violin() draws them. Giggly has none of this yet.

Violins by number of cylinders

p <- ggplot(mtcars, aes(factor(cyl), mpg))
p + geom_violin()

Not in Giggly yet: geom_violin().

Horizontal violins

# Orientation follows the discrete axis
ggplot(mtcars, aes(mpg, factor(cyl))) +
  geom_violin()

Not in Giggly yet: geom_violin().

Violins with jittered points

p + geom_violin() + geom_jitter(height = 0, width = 0.1)

Not in Giggly yet: geom_violin() and geom_jitter() with its height and width options.

Scaling the widths

# Scale maximum width proportional to sample size:
p + geom_violin(scale = "count")

# Scale maximum width to 1 for all violins:
p + geom_violin(scale = "width")

By default every violin has the same area, scale = "area".

Not in Giggly yet: geom_violin() and its scale option.

Untrimmed tails

# Default is to trim violins to the range of the data. To disable:
p + geom_violin(trim = FALSE)

Not in Giggly yet: geom_violin() and its trim option.

A smaller bandwidth

# Use a smaller bandwidth for closer density fit (default is 1).
p + geom_violin(adjust = .5)

adjust multiplies the bandwidth the density estimate would otherwise use.

Not in Giggly yet: geom_violin() and its adjust option.

Mapping fill

# Add aesthetic mappings
# Note that violins are automatically dodged when any aesthetic is
# a factor
p + geom_violin(aes(fill = cyl))
p + geom_violin(aes(fill = factor(cyl)))
p + geom_violin(aes(fill = factor(vs)))
p + geom_violin(aes(fill = factor(am)))

Mapping fill to something discrete that varies within each x, as factor(vs) does, splits a violin into one for each value, dodged side by side.

Not in Giggly yet: geom_violin().

A fixed fill and colour

# Set aesthetics to fixed value
p + geom_violin(fill = "grey80", colour = "#3366FF")

Not in Giggly yet: geom_violin().

Quartiles

# Show quartiles
p + geom_violin(draw_quantiles = c(0.25, 0.5, 0.75))

ggplot2 has deprecated draw_quantiles, in favour of quantiles and quantile.linetype.

Not in Giggly yet: geom_violin() and its draw_quantiles option.

Scale and coordinate transformations

require() loads the ggplot2movies package, and the rest of the page's examples run only where it is installed. Its movies dataset holds films from the Internet Movie Database, with their rating, number of votes, year and budget.

# Scales vs. coordinate transforms -------
if (require("ggplot2movies")) {
# Scale transformations occur before the density statistics are computed.
# Coordinate transformations occur afterwards.  Observe the effect on the
# number of outliers.
m <- ggplot(movies, aes(y = votes, x = rating, group = cut_width(rating, 0.5)))
m + geom_violin()
m +
  geom_violin() +
  scale_y_log10()
m +
  geom_violin() +
  coord_transform(y = "log10")
m +
  geom_violin() +
  scale_y_log10() + coord_transform(y = "log10")

cut_width(rating, 0.5) groups the films into bins of rating half a point wide, a violin for each.

Not in Giggly yet: geom_violin(), a whole-column function in a mapping, such as cut_width(rating, 0.5), cut_width(), coord_transform(), and the movies dataset from the ggplot2movies package.

Violins along a continuous x

# Violin plots with continuous x:
# Use the group aesthetic to group observations in violins
ggplot(movies, aes(year, budget)) +
  geom_violin()
ggplot(movies, aes(year, budget)) +
  geom_violin(aes(group = cut_width(year, 10)), scale = "width")
}

Not in Giggly yet: geom_violin() and its scale option, a whole-column function in a mapping, such as cut_width(year, 10), cut_width(), and the movies dataset from the ggplot2movies package.