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RFC: log='z' for image, contour, persp?

4 messages · Duncan Murdoch, Martin Maechler, Don MacQueen

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

For example,

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

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

We already support

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

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

image(z, log="x")

fails because it tries to take a log of zero.

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

Duncan Murdoch
Martin Maechler
# 
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
Duncan Murdoch
#
On 5/10/2006 4:23 AM, Martin Maechler wrote:
Thanks for pointing that out.  This is a little tricky:  I think 
filled.contour would want evenly spaced contours, but use the axTicks() 
version of pretty labels on the legend; but contour() would probably 
want the contours themselves to be at nice round values.

It looks as though I'll need to think about adding a log=TRUE option to 
pretty(), to expose or duplicate the internal code that sets log axes. 
(axTicks is close, but I don't think it allows for automatic computation 
of axp[3]).

Duncan
Don MacQueen
# 
Yes, it does. I've needed it more often than not.
-Don
At 6:41 PM -0400 5/9/06, Duncan Murdoch wrote: