I would put your filters in to a cell array and think about how to use cellfun or arrayfun to apply them to the data.

–Loren

What I would like to be able to do in many situations is something like this:

for i=1:n

% 1) apply nth filter to raw data

% 2) save result to nth matrix of filtered data

end
I think this should be done with vectorizing of a for loop and may involve indexing. But I can't even get to write the correct for loop because I think that would require use of arrays and I am not at all familiar with those.

Could you point me in the right direction. Would this be a topic of interest for a post?
Thank you so much again.

Matteo

Although I do lots of data interpretation using Matlab, I am fairly new to programming. I have a problem and I think indexing may be the solution, but I’m stuck. I tried some of the blogs from you, Steve, Doug on indexing, but to no avail. I would appreciate any hint or pointing to some reference.

I am applying a gaussian filter to some data multiple times by increasing sigma and the size of the kernel. For example.

H24 = fspecial('gaussian',[120 120],24);
lowp24 = imfilter(zeg1,H24,'replicate');

H25 = fspecial('gaussian',[125 125],25);
lowp25 = imfilter(zeg1,H25,'replicate');

I could not figure out a way to avoid doing it by hand – I have about 50 gaussian filters. I thought, no big deal, have to get the job done. But now I’d like to try the differencers between consecutive results (say lowp25-lowp24) to understand when I’m getting no further improvement. You can see where this is going. I have to do this kind of operations often and would like an idea on how to write code to streamline my workflow.

Thank you.
Matteo

A singleton dimension contains only 1 index in that dimension, e.g., A(3:5,17,2:3) has the 2nd dimension as a singleton since the size of this array would be 3x1x2.

–Loren

MATLAB doesn’t currently support the syntax you’d like to use. You must do the variable assignment and then index into the result.

–Loren

The part of code I can’t get working is ‘randperm(end)(1:3)’. I want the first three random elements from matrix A. I could get the same result with the code:
A = [21 23 24 25 26];
idx = randperm(length(A));
B = A( idx(1:3) );
but I would prefer not to use the additional variable ‘idx’.

Thanks in advance,
Pieter Laurens

Glad you were able to get your code working. Perhaps it would be worth posting the new version here for people to compare.

I fixed your code by reinserting the > and < . However, it doesn't look identical to the code you posted to the newsgroup (an if-end chunk missing). FYI, the software doesn't remove >,< if they are inside the html pre tags.

–Loren

incidentally, the code i posted worked fine, i just thought it was ugly and knew you would know of a better way. it does have comments that describe its specification and i think they are pretty simple, plus i posted a reference to the matlab documentation that explains the algorithm. i did not know that pre tags were necessary to prevent the blog software from mangling code (i guess less than and greater than signs are dangerous on the web) — i merely pasted in text from my m-file editor. anyway, the code pasted fine into that matlab forum at:
http://newsreader.mathworks.com/WebX?14@896.8e9dbxh5WSs@.ef47e04

it looks like this blog software removes anything between a less than or equal sign and the next greater than sign (even if that is several lines later) from your readers’ posts. just fyi.

thanks again,
-erik