MATLAB: How to convert a string which contains a variable name into a variable which can be called

stringstringsvariablevariables

I am creating a function which scans files for a certain function and determines which variables (all are already initialized) are used as parameters for the function. Currently, I am able to derive a cell array with strings for each individual variable. The program takes this:

x = DummyFunction(a, b, c);

And returns this:

{'a'} {'b'} {'c'}

I am trying to convert these strings, which contain pre-established variables, into variables which can be called. Any suggestions?

Thanks in advance, Ak

Best Answer

You do not need to do that.

Put all of the variables into a structure, using dynamic field names. Then when you need to recall them by name,

   Variables_for_this_call = cellfun(@(name) StructureOfVariables.(name), ListOfNames, 'uniform', 0);

After which you can

DummyFunction(Variables_for_this_call{:})

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MATLAB: I have a .mat file with field names like c0_Curve_Someheadername. When I load the .mat file into Matlab it reorders the files in a differ sequential order (c0_Curve_Header1; c10_Curve_Header10; etc). Is there an eas way to reorganize the field name

Your code needs a few improvements before getting to the main task:

Instead of load-ing directly into the workspace you should load directly into an output variable (which is a structure).
Use fullfile to generate filenames from parts.
Do NOT use the variable name path, because you shadow the inbuilt (and very important) path function.
Do NOT use eval to access variable names. Using eval to access variable names is how beginners force themselves into writing slow, buggy, complex 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

These are trivially fixed. For example, loading the data like this:

S = load(fullfile(fpth,fnm));

And then it is trivial to get the fieldnames into alphanumeric order: download my FEX submission natsort, which probably gives the order that you want (if not please clearly explain the required order):

C = fieldnames(S);
C = natsort(C);
for k = 1:numel(C)
    data = S.(C{k})
    ...
end

or together with orderfields you could even change the order of the fields in the structure itself:

S = ordefields(S,C);

Notice that it is not actually required to change the order of the fields to access them, once you have cell array C in the correct order. Alternatively you could use the second output of natsort, which is an index of the sort order.

Do you notice how much simpler all of these options are, compared to dynamically accessing variable names?

MATLAB: Adding elements into a vector using MATLAB GUI

You have

x=[];
y=[];

so you set x and y to empty arrays

a=str2double(get(handles.edit1,'string'));
b=str2double(get(handles.edit2,'string'));

so you get scalar a and b values from what the user entered

handles.x=[x a];
handles.y=[y b];

x and y are both empty because you set them that way, so this is equivalent to

handles.x = a;
handles.y = b;

which sets scalars. But it sounds like later you expect handles.x and handles.y to be a record of everything the user ever entered.

I suspect you want

if ~isfield(handles, 'x')
  handles.x = [];
  handles.y = [];
end
 a = str2double(get(handles.edit1,'string'));
 b = str2double(get(handles.edit2,'string'));
 handles.x(end+1) = a;
 handles.y(end+1) = b;
 guidata(hObject, handles);

Note: in your callbacks, the lines

handles.x;
handles.y;

are not doing anything useful and can be removed.

Best Answer

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MATLAB: I have a .mat file with field names like c0_Curve_Someheadername. When I load the .mat file into Matlab it reorders the files in a differ sequential order (c0_Curve_Header1; c10_Curve_Header10; etc). Is there an eas way to reorganize the field name

MATLAB: Adding elements into a vector using MATLAB GUI

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