Re: [R] "10^k" axis labels {was ".. (log scale on y-axis)"}

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Fri 01 Jul 2005 - 23:23:45 EST

On 7/1/05, Martin Maechler <maechler@stat.math.ethz.ch> wrote:
> >>>>> "Gabor" == Gabor Grothendieck <ggrothendieck@gmail.com>
> >>>>> on Thu, 30 Jun 2005 07:28:30 -0400 writes:
>
> Gabor> On 6/29/05, Jing Shen <jshen6@gmail.com> wrote:
>
> >> I am planning to plot my data on log scale (y-axis). There is a
> >> parameter in plot function, which is
> >> plot( ..., log="y", ...)
> >> While, the problem is that it is with base of e. Is there a way to let
> >> me change it to 10 instead of e?
> >>
>
> Gabor> Is your question how to get the axis labels to be powers of 10?
> Gabor> In that case,
>
> Gabor> plot(1:100, log = "y", yaxt = "n") # do not show y axis
> Gabor> axis(2, c(1,10,100)) # draw y axis with required labels
>
> and if you're there, you might be interested in the following
> which provides a somewhat automated way to show
> "a * 10 ^ k" tick-labels instead of the scientific "a e k" ones.
> { For some time, I had wanted that something like this could
> become an easy option for builtin axis(*), but then I also know
> that we should rather strive to build future-proof tools, which
> "hence" should we applicable to 'grid' as well as to old-style
> 'graphics' and all this got me stuck in the process ...
> }
>
> Martin Maechler, ETH Zurich
>
> ---------------
>
> axTexpr <- function(side, at = axTicks(side, axp=axp, usr=usr, log=log),
> axp = NULL, usr = NULL, log = NULL)
> {
> ## Purpose: Do "a 10^k" labeling instead of "a e<k>"
> ## this auxiliary should return 'at' and 'label' (expression)
> ## ----------------------------------------------------------------------
> ## Arguments: as for axTicks()
> ## ----------------------------------------------------------------------
> ## Author: Martin Maechler, Date: 7 May 2004, 18:01
> eT <- floor(log10(abs(at)))# at == 0 case is dealt with below
> mT <- at / 10^eT
> ss <- lapply(seq(along = at),
> function(i) if(at[i] == 0) quote(0) else
> substitute(A %*% 10^E, list(A=mT[i], E=eT[i])))
> do.call("expression", ss)
> }
>
> par(mar=.1+c(5,5,4,1))## << For the horizontal y-axis labels, need more space
> plot(x,y, axes= FALSE, frame=TRUE)
> aX <- axTicks(1); axis(1, at=aX, label= axTexpr(1, aX))
> if(FALSE) # rather the next one
> { aY <- axTicks(2); axis(2, at=aY, label= axTexpr(2, aY))}
> ## or rather (horizontal labels on y-axis):
> aY <- axTicks(2); axis(2, at=aY, label= axTexpr(2, aY), las=2)

This may not be as good as what you have (although its arguably prettier in the specific example below) and may suffice in many, though possibly not all, cases -- I mention it since its very simple and, in fact, requires no auxilliary routines. It uses your idea of employing axTicks. The key trick is to use axTicks twice in axis:

 x <- 10 ^ seq(-2,10) # test data

plot(x, log = "y", yaxt = "n")
axis(2, axTicks(2), axTicks(2))



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