How do access a variable from structure based on a string name of the structure?

I have a simulink model simulating different heat producers in a house. From this simulation I get a lot of data on the demand, the different suppliers, the power consumed etc.

The idea is to be able to run multiple simulations (outputs 1, 2 etc.) and present data for a single simulation, but also be able to compare data. This means making plots with data from multiple simulations, generating some tables with relevant variable. Each simulation has the same variable names, so that is why I need a way to acess data from multiple simulations. It can also be that an input is added and then I still would like to compare it to previous performed simulations with a different amount of variables (that is why the question dissimilar structures).

S1 = load ('Outputs1' )
S2 = load ('Outputs2' )

for i = 1:2
S(i).var1
S(i).var2
end

Is something like possible? I know i can do this: fldnm = 'varnam1'; % S1.(fldnm)

but the option above i have not yet found. I want to do this since I have multiple output files with many the same variables which i want to be able to plot and compare.

[Stephen23]

This is easy when you use indexing, exactly as KSSV's answer shows. Indexing is what you should use.

This is slow, complex, and buggy if you use lots of separate variable names and try to access the dynamically (which is what you were trying to do). All experienced MATLAB users will advise you to avoid doing this. Read this to know why:

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

Answer 1

[KSSV]

Very much possible...check the below demo code:

S1.name = 'Tom' ; S1.age = 14 ;
S2.name = 'Dick' ; S2.age = 15 ;

S(1) = S1 ;
S(2) = S2 ;

for i = 1:2
    S(i).name 
    S(i).age
end

[Mattijs Mientki]

Thank you, I was not that familiar with structures, but this works great. Is it however also possible with dissimilar structures?

[Stephen23]

+1 indeed. Or skip the concatenation by using indexing in the first place:

S(1).name = 'Tom';
S(1).age = 14;
S(2).name = 'Dick';
S(2).age = 15;

Read more here: https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

"Is it however also possible with dissimilar structures?"

The fields must be the same for this to work. For dissimilar structures you will need to put them into a cell array.

[Mattijs Mientki]

The cell structure seems to work if my 2 files (Outputs1 and Outputs2)have different variables So now I have the following which works:

S1 = load (Outputs1);
S2 = load (Outputs2);
S_Cell = {S1,S2}
for i = 1:2
S_Cell{i}.var1
end

[Stephen23]

@Mattijs Mientki: another option is to only load the field that you want:

S(1) = load(Outputs1,'var1');
S(2) = load(Outputs2,'var1')
for k = 1:numel(S)
    S(k).var1
end

Accessing data in non-scalar structure is easier than accessing the data in lots of scalar structures in a cell array, so it is worth trying to do this if you can. Then you can do things like this:

{S.var1}

to put all var1 fields into one cell array. Read more here:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

[Mattijs Mientki]

But doest this is also work easily for multiple variables since I have about 50-100 variables in the files Outputs1 and Outputs2. The example you have is only for 1 varibale in both files.

[Steven Lord]

Why don't you tell us a little more about how you're planning to use those variables? With that knowledge we may be able to offer guidance on what technique or techniques will allow you to most effectively work with your data.

[Mattijs Mientki]

Sorry that I was not that clear, I update the question description to describe more clearly what I want to be able to do.