Calculate equispaced x positions.

Calculate equispaced x positions of values that have been plotted with the plot command.

Usage

tsxpos(x,xlim,nint)

Arguments

x

A vector of numeric values or a time series object created with the ts function.

xlim

Explicit x limits for the x positions.

nint

The number of intervals between x positions.

Details

tsxpos calculates equispaced x positions for a vector of values or a time series created with the ts command from the stats package. It assumes that the default x limits have been used in the existing plot. It adds the appropriate padding if 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))