These geoms add labelled reference lines to a plot, either horizontal, vertical, or diagonal (specified by slope and intercept). These are useful for annotating plots. They are the labelled equivalent of the geom_vline, geom_hline and geom_abline from ggplot2.

## Usage

geom_textabline(
mapping = NULL,
data = NULL,
slope,
intercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE
)

geom_labelabline(
mapping = NULL,
data = NULL,
slope,
intercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
straight = NULL,
label.r = unit(0.15, "lines"),
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE
)

geom_texthline(
mapping = NULL,
data = NULL,
yintercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE
)

geom_labelhline(
mapping = NULL,
data = NULL,
yintercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE,
straight = NULL,
label.r = unit(0.15, "lines"),
)

geom_textvline(
mapping = NULL,
data = NULL,
xintercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE
)

geom_labelvline(
mapping = NULL,
data = NULL,
xintercept,
stat = "identity",
position = "identity",
...,
arrow = NULL,
lineend = "butt",
na.rm = FALSE,
show.legend = NA,
inherit.aes = TRUE,
straight = NULL,
label.r = unit(0.15, "lines"),
)

## Arguments

mapping

Set of aesthetic mappings created by aes() or 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)).

slope

The slope of the abline

intercept

the point on the y axis at which the abline crosses it.

stat

The statistical transformation to use on the data for this layer, as a string.

position

Position adjustment, either as a string, or the result of a call to a position adjustment function.

...

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. These can also be the following text-path parameters:

gap

A logical(1) which if TRUE, breaks the path into two sections with a gap on either side of the label. If FALSE, the path is plotted as a whole. Alternatively, if NA, the path will be broken if the string has a vjust between 0 and 1, and not otherwise. The default for the label variant is FALSE and for the text variant is NA.

upright

A logical(1) which if TRUE (default), inverts any text where the majority of letters would upside down along the path, to improve legibility. If FALSE, the path decides the orientation of text.

halign

A character(1) describing how multi-line text should be justified. Can either be "center" (default), "left" or "right".

offset

A unit object of length 1 to determine the offset of the text from the path. If this is NULL (default), the vjust parameter decides the offset. If not NULL, the offset argument overrules the vjust setting.

parse

A logical(1) which if TRUE, will coerce the labels into expressions, allowing for plotmath syntax to be used.

straight

A logical(1) which if TRUE, keeps the letters of a label on a straight baseline and if FALSE (default), lets individual letters follow the curve. This might be helpful for noisy paths.

padding

A unit object of length 1 to determine the padding between the text and the path when the gap parameter trims the path.

text_smoothing

a numeric(1) value between 0 and 100 that smooths the text without affecting the line portion of the geom. The default value of 0 means no smoothing is applied.

rich

A logical(1) whether to interpret the text as html/markdown formatted rich text. Default: FALSE. See also the rich text section of the details in geom_textpath().

remove_long

if TRUE, labels that are longer than their associated path will be removed.

arrow

Arrow specification, as created by grid::arrow().

lineend

Line end style (round, butt, square).

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().

straight

A logical(1) which if TRUE, keeps the letters of a label on a straight baseline and if FALSE (default), lets individual letters follow the curve. This might be helpful for noisy paths.

label.r

Radius of rounded corners. Defaults to 0.15 lines.

Amount of padding around label. Defaults to 0.25 lines.

yintercept

The value at which the line should intercept the y axis

xintercept

The value at which the line should intercept the y axis

## Value

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

## Details

Although reference lines are straight, and therefore don't lend themselves to curved text, these geom layers are included in this package because they make labelling reference lines easier, allow automatic line breaking if desired, and will translate nicely into polar co-ordinates.

These geoms act slightly differently from other geoms. You can supply the parameters in two ways: either as arguments to the layer function, or via aesthetics. If you use arguments, e.g. geom_textabline(label = "my label", intercept = 0, slope = 1), then behind the scenes the geom makes a new data frame containing just the data you've supplied. That means that the lines will be the same in all facets; if you want them to vary across facets, construct the data frame yourself and use aesthetics.

Unlike most other geoms, these geoms do not inherit aesthetics from the plot default, because they do not understand x and y aesthetics which are commonly set in the plot. They also do not affect the x and y scales.

## Aesthetics

The geom_textabline(), geom_texthline() and geom_textvline() understand the following aesthetics (required aesthetics are in bold):

• label

• slope (geom_textabline() and geom_labelabline())

• intercept (geom_textabline() and geom_labelabline())

• yintercept (geom_texthline() and geom_labelhline())

• xintercept (geom_textvline() and geom_labelvline())

• alpha

• angle

• colour

• family

• fontface

• group

• hjust

• vjust

• linecolour

• lineheight

• linetype

• linewidth

• size

• spacing

• textcolour

In addition to aforementioned aesthetics, geom_labelabline(), geom_labelhline() and geom_labelvline() also understand:

• boxcolour

• boxlinetype

• boxlinewidth

• fill

The spacing aesthetic allows fine control of spacing of text, which is called 'tracking' in typography. The default is 0 and units are measured in 1/1000 em. Numbers greater than zero increase the spacing, whereas negative numbers decrease the spacing.

Other geom layers that place text on paths.

## Examples

ggplot(mtcars, aes(mpg, disp)) +
geom_point() +
geom_texthline(yintercept = 200, label = "displacement threshold",
hjust = 0.8, color = "red4") +
geom_textvline(xintercept = 20, label = "consumption threshold", hjust = 0.8,
linetype = 2, vjust = 1.3, color = "blue4") +
geom_textabline(slope = 15, intercept = -100, label = "partition line",
color = "green4", hjust = 0.6, vjust = -0.2)