geom_hline.Rd

% Generated by roxygen2 (4.0.0): do not edit by hand
\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{show_guide}{should a legend be drawn? (defaults to \code{FALSE})}

\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 layer specific dataset - only needed if you want to override
the plot defaults.}

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

\item{position}{The position adjustment to use for overlapping points
on this layer}

\item{...}{other arguments passed on to \code{\link{layer}}. This can
include aesthetics whose values you want to set, not map. See
\code{\link{layer}} for more details.}
}
\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 <- qplot(mpg, wt, data=mtcars, facets = 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
}