2-D density contours

mark_contour() draws iso-density contour lines of a 2-D point cloud (x, y); mark_contour_filled() fills the bands between them. By default the field is a kernel density estimate (needs the MASS package); map a z aesthetic to instead contour a supplied surface over a regular x/y grid. Contours are coloured by level automatically — mark_contour() maps color = after_stat(level), mark_contour_filled() maps fill. Contour tracing is done by the engine (vellum::vl_contour()), so no extra package is needed for the lines; a density field additionally needs MASS.

Usage

mark_contour(
  plot,
  ...,
  bins = 10,
  binwidth = NULL,
  breaks = NULL,
  n = 100,
  blend = NULL,
  sketch = NULL,
  data = NULL
)

mark_contour_filled(
  plot,
  ...,
  bins = 10,
  binwidth = NULL,
  breaks = NULL,
  n = 100,
  blend = NULL,
  sketch = NULL,
  data = NULL
)

Arguments

plot

A PlotSpec (from vplot()).

...

Encodings (tidy-eval): x, y (+ optional z surface, color / fill, linewidth, linetype).

bins

Target number of contour levels (when neither breaks nor binwidth is given).

binwidth

Spacing between contour levels, or NULL.

breaks

Explicit contour levels, or NULL to derive from bins / binwidth.

n

Density-estimate grid resolution per axis (KDE mode only).

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.

Value

The modified PlotSpec.

Examples

vplot(faithful) |>
  mark_point(x = eruptions, y = waiting) |>
  mark_contour(x = eruptions, y = waiting)

vplot(faithful) |> mark_contour_filled(x = eruptions, y = waiting)