MATLAB: Dynamically assign structure names and loop them in fuction

dynamically named variableevalfor loopMATLABstructures

Hello
I am trying to dynamically assign some of my variable names which are structures and them pass them through a script although I get an error
DATA=who('DATA*')
ORIG=who('ORIGINAL*')
countS=length(DATA)
countC=length(ORIG)
if countS==countC;
    for i=1:countS
figure
    scatter(DATA{i,1}.H,ORIGINAL{i,1}.H)
lm(i)=polyval(DATA{i,1}.H,ORIGINAL{i,1}.H)
    end      
end
Though i get Attempt to reference field of non-structure array. The structures themselves contain fields that i want to iterate through other processes, am I doing something wrong?
thanks

Best Answer

Avoid creating dynamically named variables in MATLAB. This is poor practice as has been explained many times on this forum, and is not recommended by MATLAB themselves:
http://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html
When you are a beginner it seems like a cunning and fast way to store information, but actually it is really bad practice to name your variables dynamically. MATLAB is also not intended for this kind of variable naming: if you continue to include data in the variable names then you will find yourself fighting many more of these battles against MATLAB.
However when you use more appropriate storage for your data (and meta-data) then you will suddenly find lots of MATLAB functions that do many useful operations for you, quickly and easily.
In your case a much more robust solution would be to use structures , where you can include fields for each kind of data (e.g. Process type, Flow data, Temperature data, Notes, Units, etc), or cell arrays . There are many functions that support working on structures and cell arrays, and can access these data easily, and they can also be used in vectorized code (which is something you need to learn about). And yes, you can even define structure fieldnames dynamically .
Placing your data in a structure or cell array also makes it much easier to pass to functions: can you imagine the fight you would have trying to pass hundreds of dynamically named variables to a function?
If you have a newer version of matlab you can also use a table , which stores the data together in one array but also allows key-name access to the columns. This might be a good alternative for your data.
In case you are interested, here are some pages explaining why dynamically assigning variable names is a really bad idea in MATLAB:
http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F
http://www.mathworks.com/matlabcentral/answers/56124-eval-is-evil-using-variables-created-dynamically-info-retrieval
http://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval
http://www.mathworks.com/matlabcentral/answers/79281-create-a-structure-name-based-on-the-string-of-a-variable-create-fieldnames-in-this-structure
http://www.mathworks.com/matlabcentral/answers/74778-loop-file-and-variablenames-when-importing
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