Significance brackets

mark_signif() runs a pairwise test between x groups and draws a significance bracket over each comparison with its p-value (or stars) — the ggsignif / ggpubr idiom. Add it on top of a mark_boxplot() / mark_violin(); the brackets stack above the data and the y-axis expands to fit them.

Usage

mark_signif(
  plot,
  ...,
  comparisons = NULL,
  method = c("wilcox.test", "t.test"),
  label = c("p", "stars"),
  step = 0.12,
  tip_length = 0.03,
  blend = NULL,
  sketch = NULL,
  data = NULL
)

Arguments

plot

A PlotSpec (from vplot()).

...

Encodings (tidy-eval): a categorical x and the numeric y.

comparisons

A list of length-2 character vectors naming the group pairs to test, e.g. list(c("a", "b"), c("b", "c")). NULL (default) tests each adjacent pair of levels.

method

The two-sample test: "wilcox.test" (default) or "t.test".

label

"p" (default, a formatted p-value) or "stars" (*/**/***/****/ns).

step

Vertical gap between stacked brackets, as a fraction of the data's y range (default 0.12).

tip_length

Bracket down-tick length, as a fraction of the y range (default 0.03).

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

set.seed(1)
d <- data.frame(g = rep(c("a", "b", "c"), each = 30),
                y = c(rnorm(30), rnorm(30, 1), rnorm(30, 0.4)))
vplot(d) |>
  mark_boxplot(x = g, y = y) |>
  mark_signif(x = g, y = y, comparisons = list(c("a", "b"), c("a", "c")))