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Opening mat files with uiopen and copying data to array

Asked by banco freno on 17 Apr 2019
Latest activity Commented on by Walter Roberson
on 18 Apr 2019
I have some mat files organized as cell arrays. All my mat files have the same structure and have progressive names, like MyFile_001, MyFile_002 and so on.
Copying data to arrays is an easy operation, such as
load('MyFile_001.mat')
Data1 = MyFile_001.Y(1).Data;
Data2 = MyFile_001.Y(2).Data;
but what if I want to choose which mat file to open instead of 'MyFile_001'?
The first row becomes
uiopen('load')
so I choose through GUI the file to be opened. How can I save data to arrays now?

  1 Comment

It is not clear from your question: do the structures (very unfortunately) all have the same names as the file names (e.g. MyFile_001), or do they (sensibly) all have the same name (e.g. Y)?

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3 Answers

Answer by Stephen Cobeldick on 18 Apr 2019
Edited by Stephen Cobeldick on 18 Apr 2019
 Accepted Answer

It seems that whoever created those .mat files unfortunately named each structure with the same name as the filename, which just makes accessing the data more complex (it is much simpler to process a sequence of .mat files when their variable names are the same for each file).
Assuming that each .mat file contains exactly one variable (i.e. the structure), then you can work with these badly designed .mat files by ignoring the variable name entirely:
T = load(...);
T = struct2cell(T);
Data1 = T{1}.Y(1).Data;
Data2 = T{1}.Y(2).Data;
See also:

  1 Comment

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Answer by Bob Nbob
on 17 Apr 2019

It seems like your issue isn't so much opening specific files, but identifying new variables. With a bit of trickery you can identify what variables are new using who.
A = who;
uiopen;
Aprime = who;
new = cellfun(@(x) sum(ismember(A,x)),Aprime,'UniformOutput',0);
new = [Aprime([new{:}]~=1)];

  1 Comment

Introspective programming (e.g. who) is slow and complex. See:
Simpler and more efficient to simply load into an output variable.

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Answer by Walter Roberson
on 17 Apr 2019

[filename, pathname] = uigetfile('*.mat');
if isnumeric(filename); error('cancel'); end
fullname = fullfile(pathname, filename);
datastruct = load(fullname, 'Y');
Data1 = datastruct.Y(1).Data;
Data2 = datastruct.Y(2).Data;

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Show 1 older comment
I get this error message: Reference to non-existent field 'Y'
The mat files contain many fields and Y is one of them. Why do I get this message?
"The mat files contain many fields and Y is one of them. Why do I get this message?"
Because this answer does not take into account the description of your .mat files, which apparently contain nested structures with the variable name the same as the filename (i.e. the files contain badly designed data).
[filename, pathname] = uigetfile('*.mat');
if isnumeric(filename); error('cancel'); end
fullname = fullfile(pathname, filename);
datastruct = load(fullname);
fn = fieldnames(datastruct); %data is stored in a struct named for the file
Data1 = datastruct.(fn{1}).Y(1).Data;
Data2 = datastruct.(fn{1}).Y(2).Data;

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