geom_hline.Rd

% Generated by roxygen2 (4.1.1): do not edit by hand
% Please edit documentation in R/geom-hline.r
\name{geom_hline}
\alias{geom_hline}
\title{Horizontal line.}
\usage{
geom_hline(mapping = NULL, data = NULL, stat = "hline",
  position = "identity", show_guide = FALSE, ...)
}
\arguments{
\item{mapping}{The aesthetic mapping, usually constructed with
\code{\link{aes}} or \code{\link{aes_string}}. Only needs to be set
at the layer level if you are overriding the plot defaults.}

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

\item{stat}{The statistical transformation to use on the data for this
layer, as a string.}

\item{position}{Postion adjustment, either as a string, or the result of
a call to a position adjustment function.}

\item{show_guide}{should a legend be drawn? (defaults to \code{FALSE})}

\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.
  }}
}
\description{
This geom allows you to annotate the plot with horizontal lines (see
\code{\link{geom_vline}} and \code{\link{geom_abline}} for other types of
lines).
}
\details{
There are two ways to use it. You can either specify the intercept of
the line in the call to the geom, in which case the line will be in the
same position in every panel. Alternatively, you can supply a different
intercept for each panel using a data.frame. See the examples for the
differences
}
\section{Aesthetics}{

\Sexpr[results=rd,stage=build]{ggplot2:::rd_aesthetics("geom", "hline")}
}
\examples{
p <- ggplot(mtcars, aes(x = wt, y=mpg)) + geom_point()

p + geom_hline(aes(yintercept=mpg))
p + geom_hline(yintercept=20)
p + geom_hline(yintercept=seq(10, 30, by=5))

# With coordinate transforms
p + geom_hline(aes(yintercept=mpg)) + coord_equal()
p + geom_hline(aes(yintercept=mpg)) + coord_flip()
p + geom_hline(aes(yintercept=mpg)) + coord_polar()

# To display different lines in different facets, you need to
# create a data frame.
p <- ggplot(mtcars, aes(mpg, wt)) +
     geom_point() +
     facet_wrap(vs ~ am)

hline.data <- data.frame(z = 1:4, vs = c(0,0,1,1), am = c(0,1,0,1))
p + geom_hline(aes(yintercept = z), hline.data)
}
\seealso{
\code{\link{geom_vline}} for vertical lines,
 \code{\link{geom_abline}} for lines defined by a slope and intercept,
 \code{\link{geom_segment}} for a more general approach
}