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

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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

Accepted Answer

per isakson
per isakson on 9 Jan 2015
Edited: per isakson on 9 Jan 2015
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"
  8 Comments
Moritz Plinke
Moritz Plinke on 14 Feb 2020
Edited: Moritz Plinke on 14 Feb 2020
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' ) )

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