Hi, Being a novice to R, I would like to create a graph in R with 2 axes. One of the 2 only has positive values, the other one also has negative values. The part I'm struggling with is how to align the 2.
Rather than starting to plot the data from the x axis, I would like to start plotting the positive values on the right axis only as of the 0 value on the left axis. Using a simple example found online, I understand how to get 2 axis on a single drawing, but I'm unsure how to accomplish the alignment objective. In the example, the 0 value of the right axis should align with the 0 of the left axis, and the red line should start in the middle of the graph only, rather than at the bottom of it. (This is an arbitrary example - the right axis could also start as of value 1000, in which case I'd like 1000 to align with 0 of the left axis.) Code: # set up some fake test data time <- seq(0,72,12) betagal.abs <- c(0.05,-0.18,0.25,0.31,0.32,0.34,0.35) cell.density <- c(0,1000,2000,3000,4000,5000,6000) #add extra space to right margin of plot within frame par(mar=c(5, 4, 4, 4) + 0.1) # Plot first set of data and draw its axis plot(time, betagal.abs, pch=16, axes=F, ylim=c(-1,1), xlab="", ylab="", type="b",col="black", main="Mike's test data") axis(2, ylim=c(-1,1),col="black") mtext("Beta Gal Absorbance",side=2,line=2.5) box() # Allow a second plot on the same graph par(new=T) # Plot the second plot and put axis scale on right plot(time, cell.density, pch=15, xlab="", ylab="", ylim=c(0,7000), axes=F, type="b", col="red") mtext("Cell Density",side=4,col="red",line=2.5) axis(4, ylim=c(0,7000), col="red",col.axis="red") # Draw the time axis axis(1,pretty(range(time),10)) mtext("Time (Hours)",side=1,col="black",line=2.5) # Add Legend legend(5,7000,legend=c("Beta Gal","Cell Density"),text.col=c("black","red"),pch=c(16,15),col=c("black","red")) Thanks in advance for any help you can provide! Best regards, Frederik Vanrenterghem ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.