Looping command for vectors with common string prefix

Dear all,

I need to iterate the same command for a list of vectors with common string prefix and a different number that characterise each. For instance, I have a market average "avilliq" and a list of vectors named milliq1, milliq2, ... , milliq91.

I need to run a MS_Regress_Fit and extract the parameters for each of these vectors. The code for one of them would be something like:

lnavilliq(isnan(lnavilliq))=[];
milliq1(isnan(milliq1))=[];
% Matrix of dependent vars
c = [lnavilliq milliq1];
dep= c; % Defines the dependent variables in system
constVec=ones(length(dep),1);
indep{1}=constVec;
indep{2}=[constVec lnavilliq];
S{1}=[1 1];
S{2}=[1 1 1];
k=2; % Number of states/regimes 
[Spec_Out_1]=MS_Regress_Fit(dep,indep,k,S,advOpt);
% Extract vector of parameters (betas)
c_high=Spec_Out_1.param(9);
c_low=Spec_Out_1.param(10);
beta2_high = Spec_Out_1.param(11);
beta2_low = Spec_Out_1.param(12);
%Extracts transition matrix from parameter vector 
beta2_p11=Spec_Out_1.Coeff.p(1);
beta2_p22=Spec_Out_1.Coeff.p(4);

I need to iterate Spec_out_# for each milliq# and then extract the parameters c_high_#, c_low_# and so on.

Any suggestion?

Thanks

SG

[dpb]

Suggestions? Yeah, do NOT even think about doing this in earnest! :)

Answer_172980 for why not and how to avoid...

[Stefano Grillini]

Thank you for your answer. While the drawbacks are clear to me now, I'm still a novice of Matlab. For example, I have imported my csv database as table into Matlab. In order to work with the arrays, I need to call them from the database as :

 milliq1 = data.PortAvilliq1;

Since I have 25 arrays to use, I've tried:

 numArrays = 25;
milliq = cell(numArrays,1);
for n = 1:numArrays
    milliq{n} = data.PortAvilliq(n);
end

But this doesn't work. Where is the problem?

Thanks

[Stephen23]

"Any suggestion?"

Do NOT do that. Magically accessing/defining variabel names is one way that beginners force themselves into writing slow, complex, buggy code that is hard to debug. Read this to know more:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

"Where is the problem?"

If the fieldname is PortAvilliq1, then your code will not magically add some number onto the end of the fieldname:

data.PortAvilliq(n)

What your code actually does is accesses n-th element of the field named PortAvilliq. Because this field (probably) does not exist you get an error. See my answer to know how to define the fieldname dynamically.

Answer 1

[Stephen23]

numArrays = 25;
milliq = cell(numArrays,1);
for n = 1:numArrays
    fld = sprintf('PortAvilliq%d',n);
    milliq{n} = data.(fld);
end

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

You should also read about fieldnames. Oh, and definitely avoid dynamically accessing any variable names.

[Stefano Grillini]

As fast as light!