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

From: Martin Maechler <maechler_at_stat.math.ethz.ch>
Date: Fri 01 Jul 2005 - 22:57:42 EST

>>>>> "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)



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