mark_boxplot: Add a boxplot mark

In glyph: A Grammar of Interactive Graphics

Add a boxplot mark

Description

Draws one box per group: the box spans the first to third quartile, the line inside it is the median, and the whiskers reach the most extreme values within coef times the interquartile range of the box. Values beyond the whiskers are drawn as outlier points.

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 box. Mapping color to a different variable than x places one box per colour side by side within each x group.

The statistics are computed in R when the plot is compiled, using stats::quantile() with its default type = 7. Rows with a missing x or y are dropped first, with a warning.

Usage

mark_boxplot(
  spec,
  ...,
  data = NULL,
  style = list(),
  coef = 1.5,
  outliers = TRUE,
  width = 0.7
)

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
coef	Length of the whiskers as a multiple of the interquartile range. Use Inf to extend them to the minimum and maximum.
outliers	Whether to draw values beyond the whiskers as points.
width	Width of each box as a fraction of the space for its group, between 0 and 1.

Value

Modified glyph_spec object with the boxplot mark added

Examples

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

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