mark_violin: Add a violin mark

In glyph: A Grammar of Interactive Graphics

Add a violin mark

Description

Draws the distribution of a numeric variable for each group as a mirrored kernel density curve, trimmed to the range of the group's values. All violins in the mark use the same density scale, so their widths can be compared directly.

Map y to the numeric variable and x to the grouping variable, which is treated as categorical even when it is numeric. Without x, all rows form one violin. Mapping color to a different variable than x places one violin per colour side by side within each x group.

The densities are computed in R when the plot is compiled, with stats::density(). A group needs at least two distinct values; groups with fewer are left out with a warning.

Usage

mark_violin(
  spec,
  ...,
  data = NULL,
  style = list(),
  bw = "nrd0",
  adjust = 1,
  width = 0.9
)

Arguments

spec	A glyph_spec
...	Aesthetic mappings: y (required, numeric), x and color.
data	Optional per-mark data override
style	Named list of fixed visual properties
bw	Smoothing bandwidth, passed to stats::density(): a number or the name of a bandwidth rule such as "nrd0" (the default) or "SJ".
adjust	Multiplier for the bandwidth. Values above 1 give smoother curves.
width	Width of the widest violin as a fraction of the space for its group, between 0 and 1.

Value

Modified glyph_spec object with the violin mark added

Examples

glyph(mtcars, x = factor(cyl), y = mpg) |>
  mark_violin()

glyph documentation built on Oct. 21, 2026, 5:12 p.m.