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Annotate a reference line

Source: R/reference_line.R
reference_line.Rd

Draws one or more reference lines within the panel, with style defaults taken from the axis.line element of the set theme.

Usage

reference_line(
  xintercept = NULL,
  yintercept = NULL,
  colour = NULL,
  linewidth = NULL,
  linetype = "dashed",
  arrow = NULL,
  layout = NULL
)

Arguments

xintercept

One or more x positions for vertical reference lines, in data coordinates or wrapped in I() for normalised panel coordinates (npc). May be a vector; each value produces a separate line.

yintercept

One or more y positions for horizontal reference lines, in data coordinates or wrapped in I() for normalised panel coordinates (npc). May be a vector; each value produces a separate line.

colour

Inherits from axis.line in the set theme. May be a vector the same length as the total number of lines.

linewidth

Inherits from axis.line in the set theme. Supports rel(). May be a vector the same length as the total number of lines.

linetype

Defaults to "dashed". May be a vector the same length as the total number of lines.

arrow

A grid::arrow() specification, or a list the same length as the total number of lines. Must use list() not c() when supplying multiple values. E.g. grid::arrow(angle = 15, length = unit(1.5, "mm"), type = "closed").

layout

Controls which panels the annotation appears in. NULL (default) repeats in all panels. An integer targets a specific panel. "fixed" repeats in all panels ignoring faceting variables. See ggplot2::layer() for full details.

Value

A list of ggplot2 annotation layers.

Details

The arrow (if any) points in the positive direction by default — rightward for xintercept lines, upward for yintercept lines.

See also

axis_line(), axis_ticks(), axis_text(), axis_bracket(), panel_shade()