Question

In order to generate a layout with multiple plots, I have the following code with some dummy plots:

jpeg("/path/to/file",height=10000,width=5000)
plot.new()
par(mar=c(2,2,1,1), oma=c(2,4,0,0), xpd=NA)

for (i in 1:10) {

    par(mar=c(2,2,1,1),fig=c(0, 0.5, (10-i)/10, (11-i)/10), new=T)    
    matplot(rnorm(20)*sample(100,1),                                          
        col="blue",axes=F,type="l",lwd=10, xlab="",ylab="")

    par(mar=c(2,2,1,1),fig=c(0.5, 1, (10-i)/10, (11-i)/10), new=T)    
    matplot(rnorm(20)*sample(100,1),                                          
        col="red",axes=F,type="l",lwd=10, xlab="",ylab="")    
}
dev.off()

I want to add a vertical line/axis on the far LHS and the far RHS that span all 10 plots in a column. Since I will use this line as an axis, I need to be able to add ticks and labels.

Answer 1

You could draw axis by ?axis or ?Axis. To span your axis on multiple plots you have to reset the usr coordinates.

Please find a base graphics solution below:

## store number of rows
nRow <- 10

## your example code 
## (only the number "10" is replaced by nRow and oma is adapted)
plot.new()

par(mar=c(2, 2, 1, 1), oma=c(2, 4, 0, 4), xpd=NA)

for (i in 1:nRow) {

    par(mar=c(2, 2, 1, 1), fig=c(0, 0.5, (nRow-i)/nRow, ((nRow+1)-i)/nRow), new=TRUE)    
    matplot(rnorm(20)*sample(100, 1),                                          
            col="blue", axes=F, type="l", lwd=10, xlab="", ylab="")

    par(mar=c(2, 2, 1, 1), fig=c(0.5, 1, (nRow-i)/nRow, ((nRow+1)-i)/nRow), new=TRUE)
    matplot(rnorm(20)*sample(100, 1),                                          
            col="red", axes=F, type="l", lwd=10, xlab="", ylab="")    
}

## define new user coordinates
usr <- c(0, 1, 0, 1) ## x1, x2, y1, y2

## calculate tick positons
## in general: (usr[3]+(diff(usr[3:4])/(nRow-1))*0:(nRow-1))
## but our usecase is much easier:
ticksAt <- 1/(nRow-1)*0:(nRow-1)

## choose left column and reset user plotting area (usr)
par(mar=c(2, 2, 1, 1), fig=c(0, 0.5, 0, 1), usr=usr, new=TRUE)
## draw axis; see ?Axis for details
Axis(side=2, at=ticksAt, labels=as.character(1:(nRow)), line=0.5)

## choose right column and reset user plotting area (usr, not needed because already done)
par(mar=c(2, 2, 1, 1), fig=c(0.5, 1, 0, 1), usr=usr, new=TRUE)
## draw axis; see ?Axis for details
Axis(side=4, at=ticksAt, labels=as.character((nRow+1):(2*nRow)), line=0.5)