[R] Axis/Ticks/Scale

[Martin Maechler]

>>>>> "Marc" == Marc Schwartz (via MN) <mschwartz at mn.rr.com>
>>>>>     on Wed, 28 Dec 2005 15:46:37 -0600 writes:

    Marc> On Wed, 2005-12-28 at 20:15 +0000,
    Marc> R.C.GILL at soton.ac.uk wrote:
    >> Dear All,
    >> 
    >> Apologies for this simple question and thanks in advance
    >> for any help given.
    >> 
    >> Suppose I wanted to plot 1 million observations and
    >> produce the command
    >> 
    >> plot(rnorm(1000000))
    >> 
    >> The labels of the xaxis are 0, e+00 2 e+05 etc. These are
    >> clearly not very attractive (The plots are for a
    >> PhD. thesis).
    >> 
    >> I would like the axes to be 0,2,4,6,8,10 with a *10^5 on
    >> the right hand side.
    >> 
    >> Is there a simple command for this?
    >> 
    >> Best Wishes
    >> 
    >> Roger


    Marc> See ?plotmath for some additional examples and there
    Marc> are some others in the list archives.

Yes, I think this one is there too:
It has the "* 10^k" after each number;
the nice thing about it is that it works for all kind of data
-- and of course, in principle it could be built into R ...



###----------------- Do "a 10^k" labeling instead of "a e<k>" ---

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)
}


x <- 1e7*(-10:50)
y <- dnorm(x, m=10e7, s=20e7)
plot(x,y)
## ^^^^^^ not so nice; ok, try 

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)