Place a ggplot legend inside the emptiest panel corner

Inspects a built plot, finds the panel corner with the fewest data points, and anchors the legend there. When no corner is clear of data (e.g. dense multi-curve panels), or the plot is faceted, the legend is sent to an outside position instead. The CORR house convention is in-panel legends placed in dead space; this automates the corner choice.

Usage

hv_legend_inside(
  plot,
  threshold = 0.08,
  box_frac = 0.3,
  pad = 0.02,
  fallback = "right",
  prefer = NULL
)

Arguments

plot: A single-panel ggplot.
threshold: Maximum fraction of data points allowed in the chosen corner box for an in-panel legend. If the emptiest corner exceeds it, fallback is used. Default 0.08.
box_frac: Corner-box size as a fraction of panel width and height (<= 0.5). Default 0.30.
pad: Inset of the legend anchor from the panel edge, in npc units. Default 0.02.
fallback: Outside legend.position used when no corner is empty enough or the plot cannot be reasoned about (facets). One of "right", "left", "top", "bottom". Default "right".
prefer: Optional preferred corner: one of "topright", "topleft", "bottomright", "bottomleft". When set and that corner is clear (its occupancy is within threshold), the legend is placed there even if another corner is emptier. If the preferred corner is occupied, the emptiest-corner logic applies as usual. Default NULL (pick the emptiest corner).

Value

The input plot with a theme layer added that sets the legend position.

Details

Apply it after the house theme (which sets legend.position = "none") so its position wins.

Examples

if (requireNamespace("ggplot2", quietly = TRUE)) {
  library(ggplot2)
  p <- ggplot(mtcars, aes(wt, mpg, colour = factor(cyl))) + geom_point()
  hv_legend_inside(p)
}