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% File src/library/grid/man/legendGrob.Rd
% Part of the R package, https://www.R-project.org
% Copyright 2013-2020 R Core Team
% Distributed under GPL 2 or later

\name{legendGrob}
\title{Constructing a Legend Grob}
\alias{legendGrob}
\alias{grid.legend}
\description{
  Constructing a legend grob (in progress)
}
\usage{
legendGrob(labels, nrow, ncol, byrow = FALSE,
           do.lines = has.lty || has.lwd, lines.first = TRUE,
           hgap = unit(1, "lines"), vgap = unit(1, "lines"),
           default.units = "lines", pch, gp = gpar(), vp = NULL)

grid.legend(\dots, draw=TRUE)
}
\arguments{
  \item{labels}{legend labels (expressions)}
  \item{nrow, ncol}{integer; the number of rows or columns, respectively
    of the legend \dQuote{layout}.  \code{nrow} is optional and
    typically computed from the number of labels and \code{ncol}.}
  \item{byrow}{logical indicating whether rows of the legend are filled first.}
  \item{do.lines}{logical indicating whether legend lines are drawn.}
  \item{lines.first}{logical indicating whether legend lines are drawn
    first and hence in a plain \dQuote{below} legend symbols.}
  \item{hgap}{horizontal space between the legend entries}
  \item{vgap}{vertical space between the legend entries}
  \item{default.units}{default units, see \code{\link{unit}}.}
  \item{pch}{legend symbol, numeric or character, passed to
    \code{\link{pointsGrob}()}; see also \code{\link[graphics]{points}} for
    interpretation of the numeric codes.}
  \item{gp}{an \R object of class \code{"gpar"}, typically the output
    from a call to the function \code{\link{gpar}}, is basically a list of
    graphical parameter settings.}
  \item{vp}{a Grid \code{\link{viewport}} object (or \code{NULL}).}
  \item{\dots}{for \code{grid.legend()}: all the arguments above are
    passed to \code{legendGrob()}.}
  \item{draw}{logical indicating whether graphics output should be produced.}
}
\value{
  Both functions create a legend \code{\link{grob}} (a graphical object
  describing a plot legend), but only \code{grid.legend} draws it (only
  if \code{draw} is \code{TRUE}).
}
%\author{Martin Maechler assisted by Marius Hofert, building on Paul Murrell's}
\seealso{
  \link{Grid}, \code{\link{viewport}};
  \code{\link{pointsGrob}}, \code{\link{linesGrob}}.

  \code{\link{grid.plot.and.legend}} contains a simple example.
}
\examples{
  ## Data:
  n <- 10
  x <- stats::runif(n) ; y1 <- stats::runif(n) ; y2 <- stats::runif(n)
  ## Construct the grobs :
  plot <- gTree(children=gList(rectGrob(),
                  pointsGrob(x, y1, pch=21, gp=gpar(col=2, fill="gray")),
                  pointsGrob(x, y2, pch=22, gp=gpar(col=3, fill="gray")),
                  xaxisGrob(),
                  yaxisGrob()))
  legd <- legendGrob(c("Girls", "Boys", "Other"), pch=21:23,
                     gp=gpar(col = 2:4, fill = "gray"))
  gg <- packGrob(packGrob(frameGrob(), plot),
                 legd, height=unit(1,"null"), side="right")

  ## Now draw it on a new device page:
  grid.newpage()
  pushViewport(viewport(width=0.8, height=0.8))
  grid.draw(gg)
}
\keyword{aplot}