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\name{tsxpos}
\title{Calculate equispaced x positions.}
\description{Calculate equispaced x positions of values that have been
plotted with the plot command.}
\usage{
tsxpos(x,xlim,nint)
}
\alias{tsxpos}
\arguments{
\item{x}{A vector of numeric values or a time series object created with
the ts function.}
\item{xlim}{Explicit x limits for the x positions.}
\item{nint}{The number of \emph{intervals} between x positions.}
}
\details{
\samp{tsxpos} calculates equispaced x positions for a vector of values or
a time series created with the \samp{ts} command from the \pkg{stats} package.
It assumes that the default x limits have been used in the existing plot. It
adds the appropriate padding if \samp{par("xaxs")} is "r". It is mainly useful
when x axis labels or some other markers are to be added to a time series plot.
A plot device must be open. If the user wishes to specify explicit x limits
or the number of intervals (not values), these will override the calculations
from the x values.
}
\value{The calculated x positions in user units.}
\author{Jim Lemon (thanks to Prof J.C. Nash for the idea)}
\examples{
# create a vector of numbers
y<-rnorm(28)
par(mfrow=c(2,1),mar=c(6,4,4,2))
plot(y,main="Plot of the values")
# convert it into a time series object
yt<-ts(y,start=2011,frequency=12)
# don't use the default axis
plot(yt,main="Plot of the time series",xaxt="n",xlab="Month")
labelpos<-tsxpos(yt)
# display an axis showing the months only
staxlab(1,labelpos,rep(month.abb,length.out=28))
par(mfrow=c(1,1),mar=c(5,4,4,2))
}
\keyword{misc}
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