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Group summary regions

Source: R/marks.R
mark_ellipse.Rd

Marks that summarise a set of (x, y) points (per group, when a color or fill is mapped) as a single enclosing region drawn over the raw points.

Usage

mark_ellipse(
  plot,
  ...,
  type = "t",
  level = 0.95,
  segments = 51L,
  blend = NULL,
  sketch = NULL,
  data = NULL
)

mark_hull(plot, ..., expand = 0, blend = NULL, sketch = NULL, data = NULL)

Arguments

plot

A PlotSpec (from vplot()).

...

Encodings (tidy-eval): x, y, and optionally color/fill (which also splits the points into per-group regions).

type

Ellipse type: "t", "norm", or "euclid".

level

Confidence level ("t"/"norm") or circle radius ("euclid").

segments

Number of line segments approximating the ellipse.

blend

Optional blend mode for compositing this layer against what is already drawn beneath it (the panel and earlier layers), one of the CSS mix-blend-mode names, e.g. "multiply", "screen", "darken". The whole layer composites as one isolated group (not per element).

sketch

A sketch() spec giving this layer a hand-drawn look (wobbly outlines, hachure fills), NA/FALSE to force it crisp (overriding a plot-wide theme_sketch()), or NULL (default) to inherit. Geometry marks accept it; text, raster, hex and datashade marks do not.

data

Optional layer data frame; overrides the plot data for this layer.

expand

For mark_hull(), grow each hull outward from its centroid by this fraction (e.g. 0.1 = 10% larger), so it encloses the markers it wraps rather than passing through their centres. 0 (default) is the tight hull.

Value

The modified PlotSpec.

Details

  • mark_ellipse() draws a covariance ellipse: a t distribution (type = "t", the default, robustly estimated via MASS), a multivariate normal ("norm"), or a Euclidean circle of radius level ("euclid"). The algorithm follows ggplot2's stat_ellipse().

  • mark_hull() draws the convex hull of the points.

Both are unfilled by default (a boundary), matching ggplot2; map or set a fill to shade the region. A region needs at least 3 points per group; smaller groups are skipped with a warning.

Examples

vplot(iris) |>
  mark_point(x = Sepal.Length, y = Sepal.Width, color = Species) |>
  mark_ellipse(x = Sepal.Length, y = Sepal.Width, color = Species)

vplot(iris) |>
  mark_point(x = Sepal.Length, y = Sepal.Width, color = Species) |>
  mark_hull(x = Sepal.Length, y = Sepal.Width, color = Species)