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ggplot2 Layer for Horizontal and Vertical Reference Lines

Source: R/geom_lines.R
geom_lines.Rd

These geoms can be used to draw horizontal or vertical reference lines in a ggplot. They use the data in the aesthetics x0 and y0 to compute their median or mean and draw them as a line.

Usage

geom_median_lines(
  mapping = NULL,
  data = NULL,
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

geom_mean_lines(
  mapping = NULL,
  data = NULL,
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes().

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

...

Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored.

  • Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data.

  • When constructing a layer using a stat_*() function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept.

  • Inversely, when constructing a layer using a geom_*() function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept.

  • The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behavior from the default plot specification.

Value

A ggplot2 layer (ggplot2::layer()) that can be added to a plot created with ggplot2::ggplot().

Aesthetics

geom_median_lines() and geom_mean_lines() understand the following aesthetics (at least one of the x0 or y0 aesthetics is required):

x0

The variable for which to compute the median/mean that is drawn as vertical line.

y0

The variable for which to compute the median/mean that is drawn as horizontal line.

alpha = NA

The alpha channel, i.e. transparency level, as a numerical value between 0 and 1.

color = "red"

The color of the drawn lines.

linetype = 2

The linetype of the drawn lines.

size = 0.5

The size of the drawn lines. Deprecated as of ggplot2 v3.4.0, use linewidth instead.

linewidth = 0.5

The width of the drawn lines. Starting at ggplot2 v3.4.0.

See also

The underlying ggplot2 geoms ggplot2::geom_hline() and ggplot2::geom_vline()

Examples

library(ggplot2)

# inherit top level aesthetics
ggplot(mtcars, aes(x = disp, y = mpg, y0 = mpg, x0 = disp)) +
  geom_point() +
  geom_median_lines() +
  geom_mean_lines(color = "blue") +
  theme_minimal()


# draw horizontal line only
ggplot(mtcars, aes(x = disp, y = mpg, y0 = mpg)) +
  geom_point() +
  geom_median_lines() +
  geom_mean_lines(color = "blue") +
  theme_minimal()


# draw vertical line only
ggplot(mtcars, aes(x = disp, y = mpg, x0 = disp)) +
  geom_point() +
  geom_median_lines() +
  geom_mean_lines(color = "blue") +
  theme_minimal()


# choose your own value
ggplot(mtcars, aes(x = disp, y = mpg)) +
  geom_point() +
  geom_median_lines(x0 = 400, y0 = 15) +
  geom_mean_lines(x0 = 150, y0 = 30, color = "blue") +
  theme_minimal()