Anyway to determine if a variable exists in a mat file (in app designer environment)?

Pulling hair out trying to find a way to check for the existence of a variable in a 200+MB mat file. I obviously don't want to load into every function and I'm trying to stear clear of the assignin and evalin commands. So far I've tried..

[app.fileName,PathName] = uigetfile('*.mat','MultiSelect','off');
 app.fileName = erase(app.fileName,".mat");
 cd(PathName);
 app.fileName;
 m = matfile(app.fileName)

This gives me a 1x1 "matlab.io.MatFile" type in the workspace. And when I try to see if a certain variable exists using "exist" or "isfield", I get logical 0. I don't know if there is a way to convert the matfile contents into a list of some sort or if there's a simpler way to check for variables. I can pull the data out of the variable with no problem but when I simply ask if it exists..

if isfield(m,'SomeVariable')
     SomeVariable = m.SomeVariable;
end

or

if exist('m.SomeVariable','var')
     SomeVariable = m.SomeVariable;
end

[Kris Hoffman]

Well after some manipulation, I've come up with this.

 % To check for the existence of a variable in a "MatFile" use "who" to generate
% A list of variables, which is turned into a string array with "string",
% Then use "strfind" to find the matching string. This will give you an index matrix.
% Then you need to see if all the numbers in the index are the same "any". If not then your 
% variable exists! Huzzah

yayNay = any(cell2mat(strfind(string(who(m)),'SomeVariable')));

I know it's a bodge, but it works. If anyone has a more elegant solution, please!

[Steven Lord]

The census.mat file contains two variables, cdate and pop.

x = matfile('census.mat');

Does 'cdate' exist in census.mat?

varIsInMat = @(name) ~isempty(who(x, name));
checkcdate = varIsInMat('cdate')

Does 'doesnotexist' exist in census.mat? [I guess I gave that one away.]

checkDNE = varIsInMat('doesnotexist')

[Paulo Fonte]

OK. who() works for matfile objects.

But it is rather strange that getfield() works even in nested structs (e,g. getfield(MatfileObj,'Geo','Name'), where . indexing doesn't, but isfield() has not the same behaviour.

Answer 1

[Steven Lord]

Use the who or whos methods of your matlab.io.MatFile object.