Add marginal distributions to a plot

add_marginal() draws a distribution of the panel's x variable along the top edge and/or of its y variable along the right edge, each sharing the main panel's axis so it lines up with the scatter (the vellumplot analogue of ggExtra::ggMarginal()). It is a plot-level modifier, like facet_wrap() or coord_flip(): it takes no encoding of its own and instead reads x, y (and, with group = TRUE, color) from the first layer that maps a numeric x and y (typically your mark_point()).

Usage

add_marginal(
  plot,
  type = c("density", "histogram"),
  sides = "tr",
  size = 0.15,
  adjust = 1,
  bins = 30,
  group = FALSE
)

Arguments

plot

A PlotSpec (from vplot()) with at least one x/y layer.

type

The marginal distribution: "density" (a kernel-density curve, the default) or "histogram" (binned counts).

sides

Which edges to draw, as a string of "t" (top, the x distribution) and/or "r" (right, the y distribution). Default "tr".

size

The marginal size as a fraction of the panel, in (0, 1).

adjust

Bandwidth multiplier for type = "density" (see mark_density()).

bins

Number of bins for type = "histogram" (see mark_histogram()).

group

When TRUE and the plot maps color/fill to a discrete variable, draw one distribution per group in the matching colour (like ggMarginal(groupColour = TRUE)). The scatter's legend already covers them, so no extra legend is added.

Value

The modified PlotSpec.

Details

The marginals are drawn without their own axes or background. This version supports a single panel only: combining it with facet_wrap() / facet_grid(), a non-Cartesian coordinate system (coord_flip(), coord_polar(), coord_fixed(), coord_sf()), or a locked aspect ratio is an error.

See also

mark_density(), mark_histogram(), facet_wrap()

Examples

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


vplot(faithful) |>
  mark_point(x = eruptions, y = waiting) |>
  add_marginal(type = "histogram", sides = "t")