在R中创建辅助y轴

Question

I had a question regarding creating secondary y-axis in R. Here is an example dataset

#generate some artifical data

per_cur <- runif(1171, 0.1, 7.62)
obs<-runif(1171,100,1000)

#create a density histogram of per_cur 

par(mfrow=c(2,1))
op <- par(mar = c(5,4,4,4) + 0.5)
hist(per_cur, prob=TRUE, border="white",main=NULL,las=1,cex.axis=0.8,ann = FALSE)
lines(density(per_cur), col="blue",lwd=2)

#add obs with a secondary y-axis

par(new = TRUE)
plot(per_cur,obs, cex=.5, pch=16, col=adjustcolor("black",alpha=0.2), axes = FALSE, ylab="Density")
axis(4,cex.axis=0.5)

It produces a plot which tells me the distribution of per_cur and also shows my the relationship between per_cur and obs through the secondary y-axis. However, when I run the following code with the only difference that I set the limit of primary y-axis using ylim=c(0,0.3) you can see the plot completely changes. It gives the impression that relationship between the obs and pre_cur is different in both plots (more obs points come under the curve in first plot compared to the second plot).

op <- par(mar = c(5,4,4,4) + 0.5)
hist(per_cur, prob=TRUE,ylim=c(0,0.3), border="white",main=NULL,las=1,cex.axis=0.8,ann = FALSE)
lines(density(per_cur), col="blue",lwd=2)
par(new = TRUE)
plot(per_cur,obs, cex=.5, pch=16, col=adjustcolor("black",alpha=0.2), axes = FALSE, ylab="Density")
axis(4,cex.axis=0.5)

I wanted to ask is there any way my secondary y-axis also get adjusted as I adjust the primary y-axis limit so that equal number of obs points are under the curve in both plots. Hope this is clear.

Answer 1

This can be accomplished by manipulating the ylim on each plot. For example:

#generate some artifical data

per_cur <- runif(1171, 0.1, 7.62)
obs<-runif(1171,100,1000)

#create a density histogram of per_cur 


# use these variables to set the limits on all plots
y1max = max(density(per_cur)$y)
y2max = max(obs)



par(mfrow=c(2,1))
op <- par(mar = c(5,4,4,4) + 0.5)
hist(per_cur, prob=TRUE, ylim = c(0, y1max), border="white",main=NULL,las=1,cex.axis=0.8,ann = FALSE)
lines(density(per_cur), col="blue",lwd=2)

#add obs with a secondary y-axis

par(new = TRUE)
plot(per_cur,obs, cex=.5, ylim = c(0, y2max), pch=16, col=adjustcolor("black",alpha=0.2), axes = FALSE, ylab="Density")
axis(4,cex.axis=0.5)

Then you scale each axis by the same factor:

# used to scale the axes
factor <- 2

op <- par(mar = c(5,4,4,4) + 0.5)
hist(per_cur, prob=TRUE, ylim = c(0, y1max * factor), border="white",main=NULL,las=1,cex.axis=0.8,ann = FALSE)
lines(density(per_cur), col="blue",lwd=2)
par(new = TRUE)
plot(per_cur,obs, cex=.5, ylim = c(0, y2max * factor),pch=16, col=adjustcolor("black",alpha=0.2), axes = FALSE, ylab="Density")
axis(4,cex.axis=0.5)