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\name{brkdn.plot}
\alias{brkdn.plot}
\title{A point/line plotting routine}
\description{Display a point/line plot of breakdowns of one or more variables.}
\usage{
brkdn.plot(vars,groups=NA,obs=NA,data,mct="mean",md="std.error",stagger=NA,
dispbar=TRUE,main="Breakdown plot",xlab=NA,ylab=NA,xaxlab=NA,
ylim=NA,type="b",pch=1,lty=1,col=par("fg"),staxx=FALSE,...)
}
\arguments{
\item{vars}{The names or indices of one or more columns in a data frame.
The columns must contain numeric data.}
\item{groups}{The name or index of a column in a data frame that classifies
the values in \samp{vars} into different, usually fixed effect, levels.}
\item{obs}{The name or index of a column in a data frame that classifies
the values in \samp{vars} into different, usually random effect, levels.}
\item{data}{The data frame.}
\item{mct}{The measure of central tendency to calculate for each group.}
\item{md}{The measure of dispersion to calculate, NA for none.}
\item{stagger}{The amount to offset the successive values at each horizontal
position as a proportion of the width of the plot. The calculated default
is usually adequate. Pass zero for none.}
\item{dispbar}{Whether to display the measures of dispersion as bars.}
\item{main}{The title at the top of the plot.}
\item{xlab,ylab}{The labels for the X and Y axes respectively. There are
defaults, but they are basic.}
\item{xaxlab}{Optional labels for the horizontal axis ticks.}
\item{ylim}{Optional vertical limits for the plot.}
\item{type}{Whether to plot symbols, lines or both (as in \samp{plot}).}
\item{pch}{Symbol(s) to plot.}
\item{lty}{Line type(s) to plot.}
\item{col}{Color(s) for the symbols and lines.}
\item{staxx}{Whether to call \link{staxlab} to display the X axis
labels.}
\item{...}{additional arguments passed to \samp{plot}.}
}
\value{
A list of two matrices of dimension \samp{length(levels(groups))} by
\samp{length(levels(obs))}. The first contains the measures of central
tendency calculated and its name is the name of the function passed as
\samp{mct}. The second contains the measures of dispersion and its name
is the name of the function passed as \samp{md}.
If both \samp{groups} and \samp{obs} are not NA, the rows of each matrix
will be the \samp{groups} and the columns the \samp{obs}. If \samp{obs}
is NA, the rows will be the \samp{groups} and the columns the \samp{vars}.
If \samp{groups} is NA, the rows will be the \samp{vars} and the columns
the \samp{obs}. That is, if \samp{vars} has more than one element, if
\samp{obs} is NA, the elements of \samp{vars} will be considered to
represent observations, while if \samp{groups} is NA, they will be
considered to represent groups. At least one of \samp{groups} and \samp{obs}
must be not NA or there is no point in using \samp{brkdn.plot}.
}
\details{
\samp{brkdn.plot} displays a plot useful for visualizing the breakdown of a
response measure by two factors, or more than one response measure by either
a factor representing something like levels of treatment (\samp{groups}) or
something like repeated observations (\samp{obs}). For example, if
observations are made at different times on data objects that receive
different treatments, the \samp{groups} factor will display the measures
of central tendency as points/lines with the same color, symbol and line type,
while the \samp{obs} factor will be represented as horizontal positions on the
plot. If \samp{obs} is numeric, its unique values will be used as the
positions, if not, 1 to the number of unique values. This is a common way of
representing changes over time intervals for experimental groups.
}
\author{Jim Lemon}
\seealso{\link{dispbars}}
\examples{
test.df<-data.frame(a=rnorm(80)+4,b=rnorm(80)+4,c=rep(LETTERS[1:4],each=20),
d=rep(rep(letters[1:4],each=4),5))
# first use the default values
brkdn.plot("a","c","d",test.df,pch=1:4,col=1:4)
# now jazz it up a bit using medians and median absolute deviations
# and some enhancements
bp<-brkdn.plot("a","c","d",test.df,main="Test of the breakdown plot",
mct="median",md="mad",xlab="Temperature range", ylab="Cognition",
xaxlab=c("10-15","16-20","21-25","25-30"),pch=1:4,lty=1:4,col=1:4)
es<-emptyspace(bp)
legend(es,legend=c("Sydney","Gosford","Karuah","Brisbane"),pch=1:4,
col=1:4,lty=1:4,xjust=0.5,yjust=0.5)
}
\keyword{misc}
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