Datashade a large point cloud — mark

For data too dense to draw one marker each (overplotted, up to millions of points), mark_datashade() bins the points into a canvas-sized grid in one pass and colours each cell by density (via vellum::datashade()), drawing a single raster that fills the panel. Cost is decoupled from point count and overplotting. Per-point colour/size aesthetics do not apply; cell colour encodes density.

Usage

mark_datashade(
  plot,
  ...,
  width = 400,
  height = 300,
  colors = NULL,
  how = "eq_hist",
  blend = NULL,
  data = NULL
)

Arguments

plot: A PlotSpec (from vplot()).
...: Encodings; x and y are required.
width, height: Aggregation grid size in cells (output raster pixels).
colors: Two or more colours forming the low-to-high density ramp. For an additive per-category overlay, ramp from a transparent/black low end to the category hue and composite with blend = "screen" (see details).
how: Density-to-colour mapping: "eq_hist" (default), "log", "cbrt", or "linear".
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).
data: Optional layer data frame; overrides the plot data for this layer.

Value

The modified PlotSpec.

Details

Categorical shading (à la datashader's count_cat) has no single-call form, but is reproduced by stacking one datashade layer per category — each with a colors ramp from black to its hue — composited with blend = "screen", so overlapping densities mix additively.

Examples

n <- 1e5
d <- data.frame(x = rnorm(n), y = rnorm(n))
vplot(d) |> mark_datashade(x = x, y = y)