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

Martin Maechler maechler at stat.math.ethz.ch
Fri Jul 1 14:57:42 CEST 2005

>>>>> "Gabor" == Gabor Grothendieck <ggrothendieck at gmail.com>
>>>>>     on Thu, 30 Jun 2005 07:28:30 -0400 writes:

    Gabor> On 6/29/05, Jing Shen <jshen6 at 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)

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