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Arrows

Source: R/geom_arrow.R
geom_arrow.Rd

This arrow geom can be used to draw lines adorned with arrow heads or fins. It is useful as an annotation layer to point to or away from other things on the plot. An arrow typically consists of three parts: the arrowhead, the shaft and fins. This geom places arrow heads at the end of a line and fins at the beginning of a line.

Usage

geom_arrow(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  ...,
  arrow_head = arrow_head_wings(),
  arrow_fins = NULL,
  arrow_mid = NULL,
  length = 4,
  length_head = NULL,
  length_fins = NULL,
  length_mid = NULL,
  justify = 0,
  force_arrow = FALSE,
  mid_place = 0.5,
  resect = 0,
  resect_head = NULL,
  resect_fins = NULL,
  lineend = "butt",
  linejoin = "round",
  linemitre = 10,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

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)).

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used the override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

  • For more information and other ways to specify the stat, see the layer stat documentation.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

...

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.

arrow_head, arrow_fins, arrow_mid

A function call to one of the arrow ornament functions that can determine the shape of the arrow head, fins or middle (interior) arrows.

length, length_head, length_fins, length_mid

Determines the size of the arrow ornaments. length sets the default length, whereas length_head, length_fins and length_mid set the lengths of the arrow head, arrow fins or middle arrows respectively. Can be one of the following:

  • A <numeric> to set the ornament size relative to the linewidth{_\*} settings.

  • A <unit> to control the ornament size in an absolute manner. Behaviour of relative units such as "npc" or "null" is undefined.

justify

A numeric(1) between [0-1] to control where the arrows should be drawn relative to the path's endpoints. A value of 0 sets the arrow's tips at the path's end, whereas a value of 1 sets the arrow's base at the path's end.

force_arrow

A logical(1) which, if TRUE an arrow will be drawn even when the length of the arrow is shorter than the arrow heads and fins. If FALSE, will drop such arrows.

mid_place

Sets the location of middle (interior) arrows, when applicable. Can be one of the following:

A numeric vector

with values between [0-1] to set middle arrows at relative positions along the arc-length of a path.

A <unit>

to fill a path with arrows with the provided unit as distance between one arrow to the next.

resect, resect_head, resect_fins

A numeric(1) denoting millimetres or <unit> to shorten the arrow. resect_head shortens the arrow from the arrow head side, whereas resect_fins shortens the arrow from the fins side. Both inherit from resect.

lineend

Line end style (round, butt, square).

linejoin

Line join style (round, mitre, bevel).

linemitre

Line mitre limit (number greater than 1).

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 behaviour from the default plot specification, e.g. borders().

Value

A <Layer> ggproto object that can be added to a plot.

Aesthetics

geom_arrow() understands the following aesthetics (required aesthetics are in bold):

Learn more about setting these aesthetics in vignette("ggplot2-specs").

See also

Other arrow geoms: annotate_arrow(), geom_arrow_chain(), geom_arrow_curve(), geom_arrow_segment()

Examples

# Setting up a plot
p <- ggplot(whirlpool(), aes(x, y, colour = group)) +
  coord_equal()

# A standard arrow
p + geom_arrow()


# Arrows can have varying linewidths
p + geom_arrow(aes(linewidth = arc))


# You can use `length_head` to decouple arrow-head size from linewidth
p + geom_arrow(aes(linewidth = arc), length_head = unit(10, "mm"))


# The arrow head shape can be controlled with the `arrow_head` argument
p + geom_arrow(arrow_head = arrow_head_line(), length_head = unit(10, "mm"))


# This works similarly for the arrow fins
p + geom_arrow(
  arrow_fins = arrow_fins_feather(),
  length_fins = unit(7, "mm")
)