\name{areaplot}
\alias{areaplot}
\alias{areaplot.default}
\alias{areaplot.formula}
\title{Area Plots}
\description{
  Produce a stacked area plot, or add polygons to an existing plot.
}
\usage{
areaplot(x, \dots)

\method{areaplot}{default}(x, y = NULL, prop = FALSE, add = FALSE, xlab = NULL,
         ylab = NULL, col = NULL, \dots)

\method{areaplot}{formula}(formula, data, subset, na.action = NULL, \dots)
}
\arguments{
  \item{x}{numeric vector of x values, or if \code{y=NULL} a numeric
    vector of y values. Can also be a 1-dimensional table (x values in
    names, y values in array), matrix or 2-dimensional table (x values
    in row names and y values in columns), a data frame (x values in
    first column and y values in subsequent columns), or a time-series
    object of class \code{ts/mts}.}
  \item{y}{numeric vector of y values, or a matrix containing y values
    in columns.}
  \item{prop}{whether data should be plotted as proportions, so stacked
    areas equal 1.}
  \item{add}{whether polygons should be added to an existing plot.}
  \item{xlab}{label for x axis.}
  \item{ylab}{label for y axis.}
  \item{col}{fill color of polygon(s). The default is a vector of gray
    colors.}
  \item{formula}{a \code{\link{formula}}, such as \code{y ~ x} or
    \code{cbind(y1, y2) ~ x}, specifying x and y values. A dot on the
    left-hand side, \code{formula = . ~ x}, means all variables except
    the one specified on the right-hand side.}
  \item{data}{a data frame (or list) from which the variables in
    \code{formula} should be taken.}
  \item{subset}{an optional vector specifying a subset of observations
    to be used.}
  \item{na.action}{a function which indicates what should happen when
    the data contain \code{NA} values. The default is to ignore missing
    values in the given variables.}
  \item{\dots}{further arguments passed to \code{matplot} and
    \code{polygon}.}
}
\value{
  Matrix of cumulative sums that was used for plotting.
}
\author{
  Arni Magnusson.
}
\seealso{
  \code{\link{barplot}}, \code{\link{polygon}}.
}
\examples{
areaplot(rpois(10,40))
areaplot(rnorm(10))

# formula
areaplot(Armed.Forces~Year, data=longley)
areaplot(cbind(Armed.Forces,Unemployed)~Year, data=longley)

# add=TRUE
plot(1940:1970, 500*runif(31), ylim=c(0,500))
areaplot(Armed.Forces~Year, data=longley, add=TRUE)

# matrix
areaplot(WorldPhones)
areaplot(WorldPhones, prop=TRUE)

# table
require(MASS)
areaplot(table(Aids2$age))
areaplot(table(Aids2$age, Aids2$sex))

# ts/mts
areaplot(austres)
areaplot(Seatbelts[,c("drivers","front","rear")],
         ylab="Killed or seriously injured")
abline(v=1983+1/12, lty=3)
}