When I tried to add lines to my graph, I became confused of how to get correct index to draw the line so that the points can be located right in the middle of the bar,below are the graph and the code I used to plot it. I wonder how to adjust the codes to make the positioning of the points better.

```
cupbp<-read.xlsx("Go.xlsx",sheet=2)
cupbp2<-subset(cupbp,PValue<0.05)
cupbp2$P.value<-log(cupbp2$PValue,base=2)
cupbp2$P.value<-abs(cupbp2$P.value)
cupbp2$bp<-substr(cupbp2$Term,12,nchar(cupbp2$Term))
opar<-par(no.readonly=T)
#
par(mar=c(5,25,7,10)+0.1)
par(cex.axis=0.6)
#This part is used to plot the bars
mybar<-barplot(height=cupbp2$P.value,names=cupbp2$bp,horiz=TRUE,las=1,xaxt="n",col="red",xlab="-log2 P value",xlim=c(0,ceiling(max(cupbp2$P.value))))
title("control vs AD up Bioprocess",line=4,adj=0.5)
axis(side=1,at=axTicks(1))
par(new=T)
#This part is used to plot the lines
plot(cupbp2$Count,mybar,type="o",pch=19,lwd=2,col="yellow",cex=1.2,ann=F,xaxt="n",yaxt="n",xlab="Gene number",)
#axis(side=3,at=c(0,pretty(max(Count),n=4)))
axis(side=3,at=axTicks(3))
mtext("Gene number",3,line=2)
par(opar)
```