Dual Y-Axis Base R Plot with different x-ticks - r

Question

I want to make a plot of 4 sets of data points using dual y-axis. The first two are on the left y-axis and last two are on the right y-axis. The first two belong to a set of numbers ranging from 5000 to 50,000. Second two sets of data belong range from 1-100. I want to plot it so that it is easily discernable that the two axis are not only on different scales but also the height between points from the two different sets with distinct ranges is obviously big. I don't want to be able to draw a horizontal line that would suggest some number from the left-y-axis can be mapped bijectively to some number on the right y-axis. I want to make it such that a horizontal line through any points from the left y-axis and right y-axis would belong to only one set related to either left or right axis.
How can I plot with 2 different y-axes?. There's
I'd use twoord.plot
From plotrix v3.7-5
by Jim Lemon but that has the disadvantage than base R beacause I can't add 4 sets of data into one plot. I can only use 2 sets of (x,y) pairs with 2--ord plot. I can theoretically plot n sets of (x,y) pairs using base R.
None
Here's what doesn't work:
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, 6) + 0.1)
## Plot first set of data and draw its axis
plot(time, betagal.abs, pch=16, axes=FALSE, ylim=c(0,1), xlab="", ylab="",
type="b",col="black", main="Mike's test data")
axis(2, ylim=c(0,1),col="black",las=1) ## las=1 makes horizontal labels
mtext("Beta Gal Absorbance",side=2,line=2.5)
box()
## Allow a second plot on the same graph
par(new=TRUE)
## Plot the second plot and put axis scale on right
plot(time, cell.density, pch=15, xlab="", ylab="", ylim=c(0,7000),
axes=FALSE, type="b", col="red")
## a little farther out (line=4) to make room for labels
mtext("Cell Density",side=4,col="red",line=4)
axis(4, ylim=c(0,7000), col="red",col.axis="red",las=1)
## Draw the time axis
axis(1,pretty(range(time),10))
mtext("Time (Hours)",side=1,col="black",line=2.5)
## Add Legend
legend("topleft",legend=c("Beta Gal","Cell Density"),
text.col=c("black","red"),pch=c(16,15),col=c("black","red"))

Answer 1

Not quite sure what you're after but you can add an extra 'line per plot' by using lines.
I've edited your code
## Plot first set of data and draw its axis
plot(time, betagal.abs, pch=16, axes=FALSE, ylim=c(0,1), xlab="", ylab="",
type="b",col="black", main="Mike's test data")
lines(seq(0, 1, 0.02), type = 'o')
axis(2, ylim=c(0,1),col="black",las=1) ## las=1 makes horizontal labels
mtext("Beta Gal Absorbance",side=2,line=2.5)
box()
## Allow a second plot on the same graph
par(new=TRUE)
## Plot the second plot and put axis scale on right
plot(time, cell.density, pch=15, xlab="", ylab="", ylim=c(0,7000),
axes=FALSE, type="b", col="red")
lines(seq(0, 5000, 10), type = 'o', col = 'red')
## a little farther out (line=4) to make room for labels
mtext("Cell Density",side=4,col="red",line=4)
axis(4, ylim=c(0,7000), col="red",col.axis="red",las=1)
which produces this:
Please let me know if this wasn't what you were after.