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% File src/library/stats/man/plot.stepfun.Rd

% Part of the R package, http://www.R-project.org

% Copyright 1995-2009 R Core Team

% Distributed under GPL 2 or later

\name{plot.stepfun}

\alias{plot.stepfun}

\alias{lines.stepfun}

\title{Plot Step Functions}

\description{

  Method of the generic \code{\link{plot}} for \code{\link{stepfun}}

  objects and utility for plotting piecewise constant functions.

}

\usage{

\method{plot}{stepfun}(x, xval, xlim, ylim = range(c(y, Fn.kn)),

     xlab = "x", ylab = "f(x)", main = NULL,

     add = FALSE, verticals = TRUE, do.points = (n < 1000),

     pch = par("pch"), col = par("col"),

     col.points = col, cex.points = par("cex"),

     col.hor = col, col.vert = col,

     lty = par("lty"), lwd = par("lwd"), \dots)

\method{lines}{stepfun}(x, \dots)

}

\arguments{

  \item{x}{an \R object inheriting from \code{"stepfun"}.}

  \item{xval}{numeric vector of abscissa values at which to evaluate

    \code{x}.  Defaults to \code{\link{knots}(x)} restricted to \code{xlim}.}

  \item{xlim, ylim}{limits for the plot region: see

    \code{\link{plot.window}}.  Both have sensible defaults if omitted.}

  \item{xlab, ylab}{labels for x and y axis.}

  \item{main}{main title.}

  \item{add}{logical; if \code{TRUE} only \emph{add} to an existing plot.}

  \item{verticals}{logical;  if \code{TRUE}, draw vertical lines at steps.}

  \item{do.points}{logical;  if \code{TRUE}, also draw points at the

    (\code{xlim} restricted) knot locations.  Default is true, for

    sample size \eqn{< 1000}.}% n = 1 + 'sample size'

  \item{pch}{character; point character if \code{do.points}.}

  \item{col}{default color of all points and lines.}

  \item{col.points}{character or integer code; color of points if

    \code{do.points}.}

  \item{cex.points}{numeric; character expansion factor if \code{do.points}.}

  \item{col.hor}{color of horizontal lines.}

  \item{col.vert}{color of vertical lines.}

  \item{lty, lwd}{line type and thickness for all lines.}

  \item{\dots}{further arguments of \code{\link{plot}(.)}, or if\code{(add)}

    \code{\link{segments}(.)}.}

}

\value{

  A list with two components

  \item{t}{abscissa (x) values, including the two outermost ones.}

  \item{y}{y values \sQuote{in between} the \code{t[]}.}

}

\author{Martin Maechler \email{maechler@stat.math.ethz.ch}, 1990,

    1993; ported to \R, 1997.}

\seealso{\code{\link{ecdf}} for empirical distribution functions as

  special step functions,

  \code{\link{approxfun}} and \code{\link{splinefun}}.

}

\examples{

require(graphics)

y0 <- c(1,2,4,3)

sfun0  <- stepfun(1:3, y0, f = 0)

sfun.2 <- stepfun(1:3, y0, f = .2)

sfun1  <- stepfun(1:3, y0, right = TRUE)

tt <- seq(0, 3, by = 0.1)

op <- par(mfrow = c(2,2))

plot(sfun0); plot(sfun0, xval = tt, add = TRUE, col.hor = "bisque")

plot(sfun.2);plot(sfun.2, xval = tt, add = TRUE, col = "orange") # all colors

plot(sfun1);lines(sfun1, xval = tt, col.hor = "coral")

##-- This is  revealing :

plot(sfun0, verticals = FALSE,

     main = "stepfun(x, y0, f=f)  for f = 0, .2, 1")

for(i in 1:3)

  lines(list(sfun0, sfun.2, stepfun(1:3, y0, f = 1))[[i]], col = i)

legend(2.5, 1.9, paste("f =", c(0, 0.2, 1)), col = 1:3, lty = 1, y.intersp = 1)

par(op)

# Extend and/or restrict 'viewport':

plot(sfun0, xlim = c(0,5), ylim = c(0, 3.5),

     main = "plot(stepfun(*), xlim= . , ylim = .)")

##-- this works too (automatic call to  ecdf(.)):

plot.stepfun(rt(50, df = 3), col.vert = "gray20")

}

\keyword{hplot}