[R] How to add a top X-axis with a different logarithmic scale?

[Itay Furman]

Thanks, Marc, for your reply.
I didn't explain myself well, but thanks to you I think I could 
phrase my question better.

I want to be able to compute new tick-positions for the top 
X-axis.

Why new ticks positions?
See in the example below (that uses your contributed minimal
code :-) what happens to the labels when you
replace 4e06 with 4.1e06.

Also, I assume from your example that using plot.new() + 
plot.window() + lines(), instead of plot() will not make a 
difference in the solution. As I mentioned in _my_ example code:
for a production I will overlay several curves and will
use lines().

	Thanks,
	Itay


#######################################################

x <- c(1.1 * 1:4, 25 * 1:5) / 50e+03
y <- c(0.15 * 1:4, 0.6 + 0.05 * 1:5)

old.par <- par(no.readonly=TRUE)
xlim <- range(x)
ylim <- c(0, 1)

plot(x, y, type = "l", log = "x", xlim = xlim, ylim = ylim)
## Replace the next line with the next-next line
axis(3, labels = axTicks(3) * 4e06)
#### axis(3, labels = axTicks(3) * 4.1e06)#<--- odd labels

par(old.par)

#######################################################


On Thu, 25 Mar 2004, Marc Schwartz wrote:

> On Thu, 2004-03-25 at 12:24, Itay Furman wrote:
> > Hi,
> > 
> > I am trying to put on one plot two different logarithmic
> > scales, using the bottom and top X-axes.
> > Below there is an example of what I am trying to achieve,
> > using axTicks() -- and fails.
> > 
> > I already spent few hours on that, and cannot figure out from
> > ?par and ?axTicks what I am doing wrong.
> > 
> > Example follows:
> > 
> > ############################################################
> 
> See my interspersed comments and then code below:
> 
> 
> > ####    Data
> > x <- c(1.1*1:4, 25*1:5) / 50e+03
> > y <- c(0.15*1:4, 0.6 + 0.05*1:5)
> > 
> > ####    Configure plot
> > old.par <- par(no.readonly=TRUE)
> > xlim <- range(xlim)
> 
> I presume the above line should be:
> 
> xlim <- range(x)
> 
> > ylim <- c(0, 1)
> > 
> > ####    Plot
> > ## For production I will plot several data sets, so I first
> > ## initialize window, and then use lines().
> > plot.new()
> > plot.window(xlim=xlim, ylim=ylim, log="x")
> > lines(x, y)
> 
> Replace the above 3 lines with:
> 
> plot(x, y, type = "l", log = "x", xlim = xlim, ylim = ylim)
> 
> > ####    Plot axes
> > axis(1)
> 
> The above axis(1) is unnecessary. The lower x axis is already created by
> plot().
> 
> > ## Ticks for upper X-axis with a new scale: xlim*4e06
> > cat("top.ticks:\n", top.ticks <- axTicks(3, usr=xlim*4e06),
> >     "\n")
> 
> I am not sure if this is what you are trying to achieve, but use:
> 
> axis(3, labels = axTicks(3) * 4e06)
> 
> This will provide for the tick marks to be in their default locations,
> just as with the lower 'x' axis, but the labels at each tick mark will
> be adjusted based upon the 4e06. You do not need to change the axis
> range to change the labels alone.
> 
> 
> > ## Here I thought to put something like axis(3, at=top.ticks).
> > ## Probably will need to rescale 'top.ticks' according to
> > ## lower X-axis? 
> > axis(2)
> 
> axis(2) is the left hand y axis and is not required here, since it too
> is already drawn by plot().
> 
> 
> > ### Restore
> > par(old.par)
> > 
> > ############################################################
> > 
> > Thanks in advance for any comments/suggestions.
> > 
> > 	Itay
> 
> 
> So, to follow up a bit more coherently, if I understand what you are
> trying to do, the code should be:
> 
> x <- c(1.1 * 1:4, 25 * 1:5) / 50e+03
> y <- c(0.15 * 1:4, 0.6 + 0.05 * 1:5)
> 
> old.par <- par(no.readonly=TRUE)
> xlim <- range(x)
> ylim <- c(0, 1)
> 
> plot(x, y, type = "l", log = "x", xlim = xlim, ylim = ylim)
> 
> axis(3, labels = axTicks(3) * 4e06)
> 
> par(old.par)
> 
> 
> 
> Does that get you what you want?
> 
> HTH,
> 
> Marc Schwartz
> 
> 
>