[R] Add text/numbers to x axis?

[Prof Brian Ripley]

On Tue, 30 May 2006, Robert Lundqvist wrote:

> Is there any simple way to add text to the x axis in R? I have tried to
> add simple characters in R without any greater sucess. As an example of
> what I want to do is the added C in the following "dumb" plot (produced
> with MacAnova using the option "dumb:T"):
>
>    ++------+-------+------+-------+------+-------+------+-------++
>   1+                              :                             *+
>    |                              :                       *  *   |
>    |                              :                 *  *         |
>    |                              :              *  .            |
> 0.8+                              :           *     .            +
>    |                              :                 .            |
>    |                              :        *        .            |
>    |                              :     *           .            |
> 0.6+                              :                 .            +
>    |                              :  *              .            |
>    |                              *                 .            |
>    |                              :                 .            |
>    |                           *  :                 .            |
> 0.4+                              :                 .            +
>    |                        *     :                 .            |
>    |                     *        :                 .            |
>    |                              :                 .            |
> 0.2+                  *           :                 .            +
>    |               *              :                 .            |
>    |         *  *                 :                 .            |
>    |*  *  *                       :                 .            |
>   0++------+-------+------+-------+------+-------+--.---+-------++
>    -2    -1.5     -1    -0.5      0     0.5      1  C  1.5      2
>
>
> My attempts to use locator() and text() in R's plot() has not been working
> as good as expected. Never really knows where the added symbols end up...

Well, they end up where you request them.  In that particular case I would
use axis() to add a label that matched the tick marks, but mtext() is 
often useful.

> BTW, anyone who knows how such "dumb" plots could be achieved in R? This
> option is avaliable in S, so a port to R shouldn't be impossible, should
> it? Don't know how to do it myself however...

There is the little matter of having access to the S source code and 
permission to make use of it, as well as knowing how the S graphics device 
model works (which AFAIK has never been publicly documented but it 
believed to be somewhat different from R).

The devil is in the details: notice how the y axis on the plot shown is 
uneven, with a stretch in the middle?  Should such things be allowed (I 
think not)?

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595