\name{panel.barchart}
\alias{panel.barchart}
\title{ Default Panel Function for barchart}
\description{
  Default panel function for \code{barchart}.
}
\usage{
panel.barchart(x, y, box.ratio = 1,
               horizontal = TRUE,
               origin = NULL, reference = TRUE,
               stack = FALSE,
               groups = NULL, 
               col = if (is.null(groups)) bar.fill$col else
               regions$col,
               \dots)
}
\arguments{
  \item{x}{ Extent of Bars. By default, bars start at left of panel,
    unless \code{origin} is specified, in which case they start there
  }
  \item{y}{ Horizontal location of bars, possibly factor}
  \item{box.ratio}{ratio of bar width to inter-bar space}
  \item{horizontal}{ logical. If FALSE, the plot is `transposed' in the
    sense that the behaviours of x and y are switched. x is now
    the `factor'.  Interpretation of other arguments change
    accordingly. See documentation of \code{bwplot} for a fuller
    explanation.
  }
  \item{origin}{ origin of the bars. For grouped displays with
    \code{stack = TRUE}, this argument is ignored and the origin set to
    0. Otherwise, defaults to \code{NULL}, in which case bars start at
    leftmost end of panel.
  }
  \item{reference}{ logical, whether a reference line is to be drawn at
    the origin
  }
  \item{stack}{ logical, relevant when groups is non-null. If
    \code{FALSE} (the default), bars for different values of the
    grouping variable are drawn side by side, otherwise they are
    stacked.
  }
  \item{groups}{ optional grouping variable}
  \item{col}{ Color of the bars. By default, the trellis parameter
    \code{bar.fill} is used if there is no grouping variable, otherwise
    \code{regions} is used. 
  }
  \item{\dots}{ extra arguments will be accepted but ignored }
}

\details{
  A barchart is drawn in the panel.
}

\seealso{
  \code{\link{barchart}}
}
\author{ Deepayan Sarkar \email{deepayan@stat.wisc.edu}}
\keyword{dplot}