[R] persp and greek symbols in the axes labels

[Prof Brian Ripley]

On Tue, 24 Jul 2007, Stephen Tucker wrote:

> I don't know why it doesn't work but I think people generally recommend that

It has never been implemented, and I believe the main reason is that the 
labels are plotted at an angle other than a multiple of 90 degrees.  Not 
all devices can do that, and rotated plotmath text can look quite ugly.

And of course this _is_ documented in ?persp

xlab, ylab, zlab: titles for the axes.  N.B. These must be character
           strings; expressions are not accepted.  Numbers will be
           coerced to character strings.

> you use wireframe() in lattice rather than persp(), because wireframe is more
> customizable (the pdf document referred to in this post is pretty good):
> http://tolstoy.newcastle.edu.au/R/e2/help/07/03/12534.html
>
> Here's an example:
>
> library(lattice)
> library(reshape)
> x <- 1:5
> y <- 1:3
> z <- matrix(1:15,ncol=3,dimnames=list(NULL,y))
> M <- melt(data.frame(x,z,check.names=FALSE),id=1,variable="y")
> wireframe(value~x*y,data=M,
>          screen=list(z=45,x=-75),
>          xlab=expression(kappa[lambda]),
>          ylab=as.expression(substitute(paste(phi,"=",true,sigma),
>              list(true=5))),
>          zlab = "Z")
>
> [you can play around with the 'screen' argument to rotate the view, analogous
> to phi and theta in persp()]

Of course, that does not rotate the labels.   If unrotated labels are 
acceptable, you can easily set up a new coordinate system (by par(usr=)) 
and call text() to put labels where you want on that.  You can even try 
rotating them via srt=.

There would be no harm in implementing this for use on devices where it 
will work: a nice self-contained project for someone who would like to 
learn about R internals.


> --- Nathalie Peyrard <Nathalie.Peyrard at toulouse.inra.fr> wrote:
>
>> Hello,
>>
>> I am plotting a 3D function using persp and I would like to use greek
>> symbols in the axes labels.
>> I  have found examples like  this one on the web:
>>
>>
> plot(0,0,xlab=expression(kappa[lambda]),ylab=substitute(paste(phi,"=",true,sigma),list(true=5)))
>>
>> this works well with plot but not with persp:
>> with the command
>>
>> persp(M,theta = -20,phi =
>>
> 0,xlab=expression(kappa[lambda]),ylab=substitute(paste(phi,"=",true,sigma),list(true=5)),zlab
>>
>> = "Z")
>>
>> I get the labels as in toto.eps
>>
>> Any suggestion? Thanks!
>>
>> Nathalie
>>
>> --
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>>
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>
>
>
>
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-- 
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