Arrow segments

geom_arrow_segment() draws a straight arrow between points (x, y) and (xend, yend). In contrast to geom_segment(), the xend and yend aesthetics default to x and y respectively, so only one of xend and yend is required.

Usage

geom_arrow_segment(
  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, either as a ggproto Geom subclass or as a string naming the stat stripped of the stat_ prefix (e.g. "count" rather than "stat_count")

position

Position adjustment, either as a string naming the adjustment (e.g. "jitter" to use position_jitter), or the result of a call to a position adjustment function. Use the latter if you need to change the settings of the adjustment.

...

Other arguments passed on to layer(). These are often aesthetics, used to set an aesthetic to a fixed value, like colour = "red" or size = 3. They may also be parameters to the paired geom/stat.

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

• x

• y

• xend or yend

• alpha

• arrow_fins

• arrow_head

• arrow_mid

• colour

• group

• linewidth

• linewidth_fins

• linewidth_head

• resect_fins

• resect_head

• stroke_colour

• stroke_width

The linewidth_fins and linewidth_head inherit from linewidth. They can be used to seperately control the start- and end-width.

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

See also

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

Examples

# Setup dummy data
set.seed(42)
df <- data.frame(
  x = LETTERS[1:6],
  y = 6:1 + rnorm(6)
)

# We can omit either `xend` or `yend` for this segment geom
p <- ggplot(df, aes(x, y = 0, yend = y, colour = x))
p + geom_arrow_segment()


# We can set the linewidth globally
p + geom_arrow_segment(aes(linewidth = y))


# Or seperately for the head and fins
p + geom_arrow_segment(aes(linewidth_head = y, linewidth_fins = 0))


# We can also place arrows in the middle
p + geom_arrow_segment(
  arrow_mid = arrow_head_line(), mid_place = c(0.33, 0.66),
  arrow_head = NULL # Turn off head
)