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Half-violin plot

Source: R/geom_violinhalf.R
geom_violinhalf.Rd

Create a half-violin plot. The half violins are drawn with ggdist::stat_slab(), so this function needs the ggdist package (version 3.3.3 or later). By default, each half violin is at most 0.45 times the spacing of the categorical axis wide (0.45 units on a discrete axis), as before. When groups are dodged, as with fill mapped to a second variable, each group takes half of its dodge cell, from the cell's centre toward its side, as in see 0.14.

Usage

geom_violinhalf(
  mapping = NULL,
  data = NULL,
  stat = "ydensity",
  position = "dodge",
  trim = TRUE,
  flip = FALSE,
  scale = c("area", "count", "width"),
  show.legend = NA,
  inherit.aes = TRUE,
  interval = FALSE,
  ...
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

stat

Kept for backward compatibility. The density is always computed by ggdist::stat_slab(), and any value other than "ydensity" or ggplot2::StatYdensity is ignored with a warning.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

trim

If TRUE (default), trim the tails of the half violins to the range of the data. If FALSE, extend the tails as ggplot2::geom_violin() does.

flip

Should the half-violin plot switch directions? By default, this is FALSE and each half violin extends to the right of its position (up, in a horizontal plot), with its flat side on the left. If flip = TRUE, all half violins extend to the left (down). Optionally, a numeric vector can be supplied indicating which specific geoms should be flipped. See examples for more details.

scale

If "area" (default), all half violins have the same area (before trimming the tails). If "count", areas are scaled proportionally to the number of observations. If "width", all half violins have the same maximum width.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

interval

Logical. If TRUE, add the median and the 66% and 95% quantile intervals of each group, drawn with ggdist::stat_slabinterval() without the slab, as in ggdist::stat_pointinterval(). Default is FALSE.

...

Other arguments passed to ggdist::stat_slab(), such as colour, fill, alpha, or adjust. As in ggplot2::geom_violin():

  • bw sets the bandwidth of the density (default "nrd0"): a number, or one of "nrd0", "nrd", "ucv", "bcv", "SJ", or "dpi".

  • kernel sets the kernel (default "gaussian").

  • bounds sets known bounds of the data, which must contain all values.

  • width (or height, in a horizontal plot) is the width of a whole violin, so each half violin is half as wide.

drop has no effect. The half violins of groups with fewer than two observations, or with all values equal, are not drawn, with a warning, but they keep their space when dodged, and their intervals are drawn. .width, point_interval, show_point, show_interval, fatten_point, arrow, and the point_ and interval_ aesthetics, such as point_size, go to the interval.

Value

A ggplot2 layer, or a list of two layers if interval = TRUE.

Examples

library(ggplot2)
library(see)

ggplot(iris, aes(x = Species, y = Sepal.Length, fill = Species)) +
  geom_violinhalf() +
  theme_modern() +
  scale_fill_material_d()


# To flip all half-violin geoms, use `flip = TRUE`:
ggplot(iris, aes(x = Species, y = Sepal.Length, fill = Species)) +
  geom_violinhalf(flip = TRUE) +
  theme_modern() +
  scale_fill_material_d()


# To flip the half-violin geoms for the first and third groups only
# by passing a numeric vector
ggplot(iris, aes(x = Species, y = Sepal.Length, fill = Species)) +
  geom_violinhalf(flip = c(1, 3)) +
  theme_modern() +
  scale_fill_material_d()


# To add the median and quantile intervals
ggplot(iris, aes(x = Species, y = Sepal.Length, fill = Species)) +
  geom_violinhalf(interval = TRUE) +
  theme_modern() +
  scale_fill_material_d()