Thread Subject:

Finding mean for changing number of variables

Hi, I'm trying to calculate the average PSD from a variable number of tests. I use the "eval" function to rename i number of variables as they are entered. (User enters no of sets, and variables are computed up to that set number using while loops). So I'm wondering how to convert this:

PSDtrimavg(:,i) = mean([PSD1trim(:,i),PSD2trim(:,i),PSD3trim(:,i)],2);

to compute the mean for any number of varialbes (PSDtrim_1...PSDtrim_i) I've tried constructing them into cell arrays, using a while loop and creating a varying length array, but the mean function can't average the correct corresponding columns.

Here's an example from one of my "new variable" loops
while i <= sets
    PSDavg = eval(['PSDAvg_' num2str(i)]);
    PSDtrim = PSDavg(floor(0.5/df+1):floor(30/df+1),:);
    eval(['PSDtrim_' num2str(i) '=PSDtrim;']);
    freqtrim = freq(floor(0.5/df+1):floor(30/df+1));
    i = i + 1;
end

Thanks for any possible help. One solution would be to creata an array of the variable names as a string and using eval to solve that, but I can't output just the variable name.

"Danny " <dmccorm2@nd.edu> wrote in message <jrvqo7$m72$1@newscl01ah.mathworks.com>...
>
>
> I use the "eval" function to rename i number of variables as they are entered.
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You're not kidding, are you?

"Danny " <dmccorm2@nd.edu> wrote in message <jrvqo7$m72$1@newscl01ah.mathworks.com>...
>
> I've tried constructing them into cell arrays, using a while loop and creating a varying length array, but the mean function can't average the correct corresponding columns.
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Elaborate on this and what you mean by "the mean function can't average the correct corresponding columns". If your data sets existed as cell array elements data{i}
why couldn't you do this

result=cellfun(@mean,data,'uni',0);

No, but I did manage to get it to work by creating variable matrices of corresponding columns, and just finding the mean across. Since there are only 5 channels of data, but potentially "infinite" tests. However, I still feel there is a more forward way of doing it.

So the way the equation is set up is to average the corresponding columns of each PSD. In other words, it averages column 1 of PSDtrim_1 with column 1 of PSDtrim_2 to make an averaged column, and then proceeds with column 2 of PSDtrim_1... The way it's stored in the cell array is each matrix entered as it's own column. Now the cell array could be anything from {1,2} to {1,99} and the mean function can't select the correct column from each subcell in a while loop. Simply put I might want to average a, b, c, d. but the mean function is only set up to do a,b,c. Another time I might want to do a,b, and mean(a,b,c) wouldn't fix that.

"Danny " <dmccorm2@nd.edu> wrote in message <jrvu16$7ri$1@newscl01ah.mathworks.com>...
>
>
> In other words, it averages column 1 of PSDtrim_1 with column 1 of PSDtrim_2 to make an averaged column, and then proceeds with column 2 of PSDtrim_1...
==============

For that to be possible, all matrices PSDtrim_i would have to be the same size. So then why couldn't you instead store your PSDs into different slices of a 3D array, i.e., so that instead of PSDtrim_i, you would have PSDtrim(:,:,i)

Then, to average together corresponding columns, all you would need to do is

result=mean(PSDtrim,3);

If this still doesn't apply to your situation, I think we need you to show us some miniature examples of PSDtrim_i, for i=1,2,3 and show what you want the output to be.

> For that to be possible, all matrices PSDtrim_i would have to be the same size. So then why couldn't you instead store your PSDs into different slices of a 3D array, i.e., so that instead of PSDtrim_i, you would have PSDtrim(:,:,i)
>
> Then, to average together corresponding columns, all you would need to do is
>
> result=mean(PSDtrim,3);
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That worked perfectly, thank you. Pretty obvious, but for whatever reason I never considered putting them 3D, probably because the original was in 2D and I was just trying to loop it.