From maechler at stat.math.ethz.ch  Wed May 10 10:23:15 2006
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Wed, 10 May 2006 10:23:15 +0200
Subject: [Rd] RFC:  log='z' for image, contour, persp?
In-Reply-To: <44611A85.8090605@stats.uwo.ca>
References: <44611A85.8090605@stats.uwo.ca>
Message-ID: <17505.41715.206150.888328@stat.math.ethz.ch>

>>>>> "Duncan" == Duncan Murdoch <murdoch at stats.uwo.ca>
>>>>>     on Tue, 09 May 2006 18:41:09 -0400 writes:

    Duncan> I've been thinking of adding the possibility of
    Duncan> including "z" among the axes to be logged in image,
    Duncan> contour, and persp.  In the first two, it would only
    Duncan> affect where the breaks were set if they are
    Duncan> calculated automatically; it would have a bigger
    Duncan> effect in persp.

    Duncan> For example,

    Duncan> image(x, y, z, log="z")

    Duncan> would set 12 colours evenly spaced on a log scale of
    Duncan> the z values.  (12 because that's the default).

    Duncan> We already support

    Duncan> image(x, y, z, log="x")

    Duncan> to scale the x axis (though there's a spurious
    Duncan> warning; I'll fix that).

    Duncan> image(z, log="x")

    Duncan> fails because it tries to take a log of zero.

    Duncan> Does it seem like a good idea for these 3D functions
    Duncan> to support log="z" the way 2D functions do?

Yes, I think it's a good idea.

You forgot to mention   filled.contour()
which is  image() + "color - legend"
For that one, it would be particularly useful to automatically
get a "evenly space in log-scale" one.

    Duncan> Duncan Murdoch

Note that for things like the above, I have added
a simple function lseq() in package 'sfsmisc' -- which I have
contemplated moving to R.  Maybe this could happen at the same
time and you could make use of it for the above.

Martin



[Rd] RFC: log='z' for image, contour, persp?
Martin Maechler