Reference lines and function curves

mark_abline() draws a sloped reference line y = slope * x + intercept across the panel (the diagonal cousin of mark_rule()'s horizontal/vertical lines). mark_function() draws a curve y = fun(x) sampled over the panel's x range — e.g. a theoretical density over a histogram, or a reference curve over a scatter. Both take no data encodings; they reuse the panel's existing x/y scales, so add them on top of a data layer. Both assume linear axes.

Usage

mark_abline(
  plot,
  ...,
  slope = 1,
  intercept = 0,
  blend = NULL,
  sketch = NULL,
  data = NULL
)

mark_function(
  plot,
  ...,
  fun,
  n = 101,
  args = list(),
  blend = NULL,
  sketch = NULL,
  data = NULL
)

Arguments

plot

A PlotSpec.

...

For mark_abline()/mark_function(), styling passed through as constants (e.g. color, linewidth, linetype).

slope, intercept

For mark_abline(), the line's slope and intercept (each may be a vector to draw several lines). Defaults 1 and 0.

blend, sketch, data

See mark_point().

fun

For mark_function(), a function (or its name) mapping a numeric x vector to y, e.g. dnorm or \(x) x^2.

n

For mark_function(), the number of points sampled across the x range. Default 101.

args

For mark_function(), extra arguments passed to fun (e.g. args = list(mean = 5, sd = 2)).

Value

The modified PlotSpec.

Examples

vplot(mtcars) |> mark_point(x = wt, y = mpg) |> mark_abline(slope = -5, intercept = 37)

vplot(data.frame(x = rnorm(200))) |>
  mark_histogram(x = x, y = after_stat(density)) |>
  mark_function(fun = dnorm)