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How do you populate a struct with multiple loaded .mat files?

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David Mabwa
David Mabwa on 29 Sep 2020
Edited: David Mabwa on 14 Oct 2020
Hi,
So I have this code below that loads my data. It works fine when not wrapped in a function, however when I wrap it in a function it doesn't work. While debugging, I can see it loading my files, however, when I get to the end of the function, they don't load onto the current workspace.
Secondly, when I assign a variable for the data files to load into, they load fine when I am only dealing with one file. When I try to load multiple files however, it doesn't run as expected. It keeps overwriting each loaded array in the struct.
I'm not at all sure what i'm doing wrong
Any help is appreciated.
Thank you!
function S=LoadData % When not wrapped in function, doesn't output S
[file,path]=uigetfile(...
{'*.m;*.mlx;*.fig;*.mat;*.slx;*.mdl',...
'MATLAB Files (*.m,*.mlx,*.fig,*.mat,*.slx,*.mdl)';
'*.jpg;*.jpeg;*.png;*.tif;*.tiff',...
'Images (*.jpg,*.jpeg,*.png,*.tif,*.tiff)'},...
'Select a File','MultiSelect','on');
if isequal(file,0)
clear file
clear path
else
if iscell(file)
for k=1:size(file,2)
S=load(fullfile(path,file{k})); % Keeps overwriting S rather than appending
end
else
S=load(fullfile(path,file));
end
clear file
clear path
end
end

Accepted Answer

Xingwang Yong
Xingwang Yong on 30 Sep 2020
There is a contradiction between your statement and your comment in code. I assume you are asking about " however when I wrap it in a function it doesn't work".
In your case, the scope of variable 'S' is limited within the function LoadData(). You can use nested function to change this behaviour.
function yourMainScript
S = [];
S = LoadData(); % now S will be in the workspace of the main script
function S=LoadData
% ...
end
end
As for overwriting, you can avoid it like this
if isempty(S)
S = load(fullfile(path,file{k}));
else
tmp = load(fullfile(path,file{k}));
for fn = fieldnames(tmp)'
S.(fn{1}) = tmp.(fn{1}); % this will overwrtie if have same fieldnames
end
end
Loop over fields of a struct can be found here:
  1 Comment
David Mabwa
David Mabwa on 14 Oct 2020
Thank you, that worked like a charm. My main issue was with the overwriting.

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