Check if variable exists in workspace to plot variable, else generate error

Hi there,

I am having some trouble with checking if a variable exists in the workspace. If the variable exists (which is a structure with time), it should plot the data in my GUI. If the variable does not exist, it should generate an error.

I used this code, however it will always generate an error even if the variable does exist in the workspace. I cannot find what I am doing wrong.

function AmechM_Callback(hObject, eventdata, handles)% Executes on button press in AmechM.

if exist('AmechM','var')
        AmechM = evalin('base','AmechM');

        plot(AmechM.time,AmechM.signals.values);
        xlabel(handles.ax1,'time (s)');
        ylabel(handles.ax1,'Acceleration (rad/s²)');
else
        errordlg('The workspace does not contain any data. Run a simulation first.','Error');
end

[per isakson]

"exists in the workspace" &nbsp which workspace, that of the callback function or the base?

[Maarten]

The base workspace.

Answer 1

[per isakson]

replace

    if exist('AmechM','var')

by

    if exist('AmechM','var') == 1

or rather by

    ise = evalin( 'base', 'exist(''AmechM'',''var'') == 1' )
    if ise

since you want to know whether AmechM exists in the base workspace

and read the on-line help on exist and on "scope"

[Maarten]

The code

ise = evalin( 'base', 'exist(''AmechM'',''var'') == 1' )
    if ise

worked, thanks!

So for my own knowledge: using

if exist('AmechM','var') == 1

only checks the existence of the variable in the callback function?

[per isakson]

"but this still does not work though" &nbsp what do you mean?

Is ise true or false when the variable exists in the base workspace?

[Maarten]

I did not see that you edited your answer before I commented. Thanks.

[per isakson]

... and see Debugging Process and Features

[per isakson]

... and I answered without reading the whole question. Happy my answer helped you.

[Aditya Kaki]

The above solution works well for variables. but its failing in detecting structure variables. eg: exist(['report.f_fun_redundant{' m '}'],'var')

If any of you have a solution could you please share . Thanks in advance.

[Moritz Plinke]

I know answer is really late but I struggled on a very similar case. My solution is using the function fieldnames().

contains( fieldnames( variable_to_inspect) , 'sub_variable_name_string' )

To make it suitable and robust for "if", use sum()

sum( contains( fieldnames( variable_to_inspect ) , 'sub_variable_name_string' ) )

[Alex Morgan]

Yes, I think fieldnames is the best solution for structures