[R] High/low level: Plot 2 time series with different axis (left and ri ght)

[SÍ Björn Hauksson]

Sun, 14 Mar 2004, Jan Verbesselt wrote:
> Dear R specialists,
> 
> I have two time series in a data.frame and want to plot them in the same
> plot(), with the left axis scaled to time series 1 (-700,0) and the
> right axis scaled to time series 2 (-0.2, 0.4). 
> 
> plot(timeserie1)
> lines(timeserie2, col=c(2)) => this one should be scaled differently
> with a new axis on the right handside.
> 
> How can these be visualised such that the fit is optimal for
> visualisation of the two time series? Which commands can I use?

I have composed a simple R function to do this. See usage example in the function description.

##
## Description: A simple function which plots two time series on one plot where 
##    the series can have different value intervals over the same time interval.
## Usage: ts.plot.2Axis(xleft, xright)
## Arguments: xleft is the time series for the left vertical axis and xright 
##     is for the right axis. xleft and xright are defined as time series with 
##     the 'ts' function in package ts.
##     ts.plot function must be available, do library(ts) to ensure this if 
##     necessary.
##     In addition the usual 'ts.plot' and 'plot' parameters can be set
##     directly (mar, main, xlab, ylab, lwd) or through gpars as in ts.plot. 
##     Also parameter digits is the preferred number of decimal digits on right 
##     axis and ticks is the preferred number of tick marks on right axis.
## Details: The time series for the right vertical axis is scaled with a simple 
##     rule of thumb scaling.
##     The ts.plot function is used to plot the series.
## Value: None. 
## Note: When scaling is not acceptable try switching the series parameters.
##     If a ylabel is to be set it is here only possible for the left axis.
## See also: 'ts.plot', 'ts', 'legend'.
## Author and date: Hauksson, Bjorn Arnar. March 2004.
## Example:
## First paste this function into the R console or use 'source'.
#library(ts)
#data(UKLungDeaths)
#x <- ldeaths
#y <- fdeaths/mdeaths
#ts.plot.2Axis(x, y)
#legTxt <- c("UK lung deaths", "UK female/male deaths (rhs)") 
#legend(1976.5, 3950, legTxt, lty=c(1:2), col=c(1:2), lwd=2, bty="n")
##

ts.plot.2Axis <- function(xleft, xright, digits=1, ticks=5, 
                          mar=(c(4,4,4,4)+0.1), main="", 
                          xlab="", ylab="", lwd=2, gpars=list()) {
	# Settings for other parameters than those in the function parameter list
	par(mar=mar)                # Margins
      k <- ncol(as.matrix(xleft)) # Number of time series on left vertical scale
	lty <- c(1:(k+1))           # Line types
	col <- c(1:(k+1))           # Line colors

	# Scale time series on right vertical axis
	scale <- (max(xleft)-min(xleft))/(max(xright)-min(xright))
      xright2 <- xright*scale
      meanScale <- mean(xleft) - mean(xright2) 
	xright2 <- xright2 + meanScale

	# Plot the series 
	ts.plot(xleft, xright2, lty=lty, col=col, main=main, ylab=ylab, xlab=xlab, 
        lwd=lwd, gpars=gpars)

	# Add the right vertical axis labels
	lab <- seq(round(min(xright), digits), round(max(xright), digits), 
        length=ticks)
	labAt <- seq(min(xright2), max(xright2), length=ticks)	
	axis(side=4, labels=lab, at=labAt)
}

Comments and suggestions for this function would be helpful. A text file with the function is available at my website, http://www.bjornarnar.net/hugbunadur/R/ts.plot.2Axis.R

Best regards,
Bjorn Arnar Hauksson
bjorn.hauksson at sedlabanki.is
http://www.bjornarnar.net/english.php