R help - Mar 2008 - Smoothing z-values according to their x, y positions

Dear All,

I'm sure this is not the first time this question comes up but I
couldn't find the keywords that would point me out to it - so
apologies if this is a re-post.

Basically I've got thousands of points, each depending on three variables:
x, y, and z.

if I do a plot(x,y, col=z), I get something very messy.

So I would like to smooth the values of z according to the values of
their neighbors (given by x and y).

Could you please point me out to the function(s) I should look into
for the smothing, and
possibly for the plotting?

Many thanks for your help,

Emmanuel

There are dozens of functions within R and contributed packages that do
this. The spatial statistics packages (see the "spatial" task view on
CRAN)
is certainly where most are concentrated, but thin plate splines (in splines
packages, I believe), tensor product splines (in mgcv package), local
likelihood (in locfit package) etc. are also available for spatial
smoothing.  Perhaps the most basic place to look is the ?loess function in
the base distribution, which will do exactly what you requested.


Bert Gunter
Genentech Nonclinical Statistics


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Emmanuel Levy
Sent: Wednesday, March 19, 2008 12:42 PM
To: r-help at r-project.org
Subject: [R] Smoothing z-values according to their x, y positions

Dear All,

I'm sure this is not the first time this question comes up but I
couldn't find the keywords that would point me out to it - so
apologies if this is a re-post.

Basically I've got thousands of points, each depending on three variables:
x, y, and z.

if I do a plot(x,y, col=z), I get something very messy.

So I would like to smooth the values of z according to the values of
their neighbors (given by x and y).

Could you please point me out to the function(s) I should look into
for the smothing, and
possibly for the plotting?

Many thanks for your help,

Emmanuel

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