From help-request at octave dot org Fri Apr 14 03:58:12 2006
Subject: Re: how do I vectorize this?
From: Claudio Belotti <bel8 at lilik dot it>
To: help at octave dot org
Date: Fri, 14 Apr 2006 10:52:18 +0200


Hi Brendan,
thank you for your reply. This is not really what I need as my data are ungridded I don't think it would be convinient to organize them in a matrix.

now, I have something like that 
z = [10; 20; 30; 40; 50]
using lookup I found 
zidx = [ 1; 3; 3; 2; 4]

these are the indexes of the matrix zi (2x2)
if I do 
zi(zidx)=z
I get zi = [10 30; 40 50]
(the 3rd value of z overwrites the 2nd one)

and I'm trying to get
zi = [10 25; 40 50]
(2nd+3rd)/2

as I wrote I do it with a for loop but I'm sure there is a better way...

thank you
Claudio



Thursday, 13 April 2006 Brendan Drew:

> You could do something like this:
> 
> F = ones(n) ./ (n.^2); // create an n x n averaging filter
> zi = filter2(F, data);
> 
> This treats your data as a 2D signal and applies an n x n averaging 
> filter (at location (i, j), you have the average over the block (i-n/2, 
> j-n/2), (i+n/2, j+n/2)).
> 
> Hope this helps.
> 
> Claudio Belotti wrote:
> 
> >Dear all,
> >I have a set of values z spread over an x-y plane
> >I want to average the values on a fixed grid (xi,yi).
> >
> >I use:
> >xidx = lookup(xi,x)
> >yidx = lookup(yi,y)
> >zidx = sub2ind(sizeofgrid, xidx, yidx)
> >
> >and then
> >
> >for i=1:length(zidx)
> >zi( zidx(i)) += z(i)
> >ni( zidx(i)) += 1
> >endfor
> >zi = zi./ni
> >
> >my question is: how do I vectorize the for-loop above?
> >
> >cheers
> >Claudio
> >
> > 
> >
> 
> 
> -- 
> Brendan Drew
> Research Scientist
> PercepTek, Inc.
> Tel: 720-344-1037 x 126
> Fax: 720-344-2360
> 12395 North Mead Way
> Littleton, CO 80125
> 



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