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:
