[R] How to get two y-axises in a bar plot?

From: Gustaf Granath <Gustaf.Granath_at_ebc.uu.se>
Date: Tue, 29 Jan 2008 17:15:03 +0100


Hi,
I have measured two response variables (y1, y2) at each treatment level (x = 0, 1.5 or 3). Now I would like to show the y1 and y2 against x in a bar plot. However, y1 and y2 differ in scale so I need two y-axises, one on the left side and one on the right side (and I dont want to standardize my responses). This is fairly easy if you want to show points,lines etc, but gets more complicated with bars.Although these kind of bar graphs are quite common, I have found very limited information about how to do them in R. I have been struggling with the barplot() command. My problem is that the bars for y1 and y2 end up at the same place (blocking each other) and not beside each other when I use par(new=TRUE). Is there a way to separate them so y1 and y2 are placed beside each other at each x level, or is this easier to do this with lattice?? I would also like to add error bars but I guess that should not be a problem.

For code and data, see below.

Cheers,

Gustaf Granath, phd student

My code so far:
#Creating data

c(6.34,13.38,17.87)->y1
c(0.85,1.88,2.33)->y2
c(0,1.5,3)->x

cbind(y1,y2,x)->mydata
data.frame(mydata)->mydata
with(mydata, tapply(y1,x,mean))->mean.y1 with(mydata, tapply(y2,x,mean))->mean.y2
#Barplot

par(mar=c(5,4,4,4)+0,1)
barplot(mean.y1,density=1,las=1)
par(new=T)
barplot(mean.y2,density=3,angle=3,axes=F) axis(4,las=1)

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