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

Question

Kris Hoffman 2018-7-10

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/409689-anyway-to-determine-if-a-variable-exists-in-a-mat-file-in-app-designer-environment

评论： Paulo Fonte 2022-1-9

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

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Steven Lord 2018-7-10

在 MATLAB Online 中打开

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 2022-1-9

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.

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