[R] plot with two y axes BUT unaligned x axis

bjmjarrett bjmjarrett at gmail.com
Wed Jun 15 13:51:00 CEST 2011


Hi all,

I have scoured the archives of this forum but nothing quite seems to fit the
bill...

I would like to plot a graph displaying two variables (y axes) that share
date as the x axis. However, the date values for each variable are not the
same - for example, some parasitoids were not released on days that
collections from the trap took place, whilst sometimes releases did occur on
the same day. I would like to align them. My code is:

####
CollectionDate<-as.Date(CollectionDate,"%m/%d/%Y") # days that had
collections
release.date.Total<-as.Date(release.date.Total,"%m/%d/%Y") # days that had
releases

par(mar=c(5,4,4,4)+0.1)

plot(CollectionDate[data$Trap=="DPAU1"],TotalP[data$Trap=="DPAU1"],type="n",ylim=c(0,80),xlab="Time",ylab="Number
of egg masses") # I am using one trap of many

lines(CollectionDate[data$Trap=="DPAU1"],TotalP[data$Trap=="DPAU1"],lwd=2)

par(new=T)

plot(release.date.Total[data$Trap=="DPAU1"],parasitoid.total[data$Trap=="DPAU1"],axes=F,type="h",lty=1,col="red",xlab="",ylab="",lwd=1.2)

axis(4,las=1)

mtext(side=4,line=3,"Total parasitoids released")
###

As in the above code, I suppressed the axes for the second plot, but if I
don't the x axis (date) has two tick marks for each year.

Is there a way to align the date objects to begin with without compromising
the graphs themselves?

Thanks in advance,

Ben

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