geom_abline.Rd

% Generated by roxygen2 (4.1.1): do not edit by hand
% Please edit documentation in R/geom-abline.r, R/geom-hline.r, R/geom-vline.r
\name{geom_abline}
\alias{geom_abline}
\alias{geom_hline}
\alias{geom_vline}
\title{Lines: horizontal, vertical, and specified by slope and intercept.}
\usage{
geom_abline(mapping = NULL, data = NULL, show.legend = NA, ..., slope,
  intercept)

geom_hline(mapping = NULL, data = NULL, show.legend = NA, yintercept, ...)

geom_vline(mapping = NULL, data = NULL, show.legend = NA, xintercept, ...)
}
\arguments{
\item{mapping}{Set of aesthetic mappings created by \code{\link{aes}} or
\code{\link{aes_}}. If specified and \code{inherit.aes = TRUE} (the
default), is combined with the default mapping at the top level of the
plot. You only need to supply \code{mapping} if there isn't a mapping
defined for the plot.}

\item{data}{A data frame. If specified, overrides the default data frame
defined at the top level of the plot.}

\item{show.legend}{logical. Should this layer be included in the legends?
\code{NA}, the default, includes if any aesthetics are mapped.
\code{FALSE} never includes, and \code{TRUE} always includes.}

\item{...}{other arguments passed on to \code{\link{layer}}. There are
  three types of arguments you can use here:

  \itemize{
  \item Aesthetics: to set an aesthetic to a fixed value, like
     \code{color = "red"} or \code{size = 3}.
  \item Other arguments to the layer, for example you override the
    default \code{stat} associated with the layer.
  \item Other arguments passed on to the stat.
  }}

\item{xintercept,yintercept,slope,intercept}{Parameters that control the
position of the line. If these are set, \code{data}, \code{mapping} and
\code{show.legend} are overridden}
}
\description{
These paired geoms and stats add straight lines to a plot, either
horizontal, vertical or specified by slope and intercept. These are useful
for annotating plots.
}
\details{
These geoms act slightly different to 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.
\code{geom_abline(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.
}
\section{Aesthetics}{

These geoms are drawn using with \code{\link{geom_line}} so support the
same aesthetics: alpha, colour, linetype and size. They also each have
aesthetics that control the position of the line:

\itemize{
  \item \code{geom_vline}: \code{xintercept}
  \item \code{geom_hline}: \code{yintercept}
  \item \code{geom_abline}: \code{slope} and \code{intercept}
}
}
\examples{
p <- ggplot(mtcars, aes(wt, mpg)) + geom_point()

# Fixed values
p + geom_vline(xintercept = 5)
p + geom_vline(xintercept = 1:5)
p + geom_hline(yintercept = 20)

p + geom_abline() # Can't see it - outside the range of the data
p + geom_abline(intercept = 20)

# Calculate slope and intercept of line of best fit
coef(lm(mpg ~ wt, data = mtcars))
p + geom_abline(intercept = 37, slope = -5)
# But this is easier to do with geom_smooth:
p + geom_smooth(method = "lm", se = FALSE)

# To show different lines in different facets, use aesthetics
p <- ggplot(mtcars, aes(mpg, wt)) +
  geom_point() +
  facet_wrap(~ cyl)

mean_wt <- data.frame(cyl = c(4, 6, 8), wt = c(2.28, 3.11, 4.00))
p + geom_hline(aes(yintercept = wt), mean_wt)

# You can also control other aesthetics
ggplot(mtcars, aes(mpg, wt, colour = wt)) +
  geom_point() +
  geom_hline(aes(yintercept = wt, colour = wt), mean_wt) +
  facet_wrap(~ cyl)
}
\seealso{
See \code{\link{geom_segment}} for a more general approach to
  adding straight line segments to a plot.
}