Dynamically rename existing structure arrays

Hi all,

I have several .mat files, each of them containing one structure array named "data" (named exactly the same in each .mat file), like the following

data = 

             hdr: [1x1 struct]
           label: {306x1 cell}
            time: {1x25 cell}

and my ultimate aim is to merge all those "data" arrays using a function (ft_appendata) of the Fieldtrip toolbox.

In order to do that, I need to have all those "data" arrays named differently from each other.

What I want to do is to create a loop which loads the files and dynamically renames the "data" arrays.

For example, having the files...

1_myfile_1.mat
1_myfile_2.mat
2_myfile_1.mat
2_myfile_2.mat  etc...

...I want to load all the files and rename each "data" variable contained in each .mat file...

for s=1:2
    for r=1:2
        load([num2str(s),'_myfile_',num2str(r),'.mat'])

          %here piece of code, which I don't know, needed for renaming the variable

      end
  end

...in order to get something like...

1_data_1 = 

             hdr: [1x1 struct]
           label: {306x1 cell}
            time: {1x25 cell}

1_data_2 = 

             hdr: [1x1 struct]
           label: {306x1 cell}
            time: {1x19 cell}

2_data_1 = 

             hdr: [1x1 struct]
           label: {306x1 cell}
            time: {1x16 cell}

etc.

I tried to use the eval() function but, as far as I have understood, it generates from scratch a new variable dynamically changing name at each iteration, while I need to simply rename an already existing structure array.

Thank you in advance for your kind help, Chiara

Answer 1

[Image Analyst]

Don't do that. Put them into an array instead.

% Read all data into different cells of a cell array
allData = cell(2, 2);   % Initialize to whatever size you need
folder = pwd; % Current folder or wherever you want.
for s = 1 : size(allData, 2)
    for r = 1 : size(allData, 1)
      baseFileName = sprintf('%d_myfile_%d.mat', s, r);
      fullFileName = fullfile(folder, baseFileName);
      if exist(fullFileName, 'file')
          storedStructure = load(fullFileName)
          % Put into cell at row r, column s:
          ca(r, s) = {storedStructure.data};
      end
    end
end

A structure array would also work. These methods are preferred over what you asked for. Why? Read the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

[Chiara Avancini]

Thank you! this worked nicely and it is also a pretty flexible solution for other types of data.

Answer 2

[Michael Haderlein]

It's not necessary to rename your variables. I suppose you want a matrix with all the structure, right? Then, the following should work:

alldata=struct('hdr',cell(2),'label',[],'time',[]);

for s=1:2
   for r=1:2
      load([num2str(s),'_myfile_',num2str(r),'.mat'])
      alldata(s,r)=data;
   end
end

Answer 3

[dpb]

Just concatenate them as you read the files...

alldat=[];    % an empty holder
for s=1:2
  for r=1:2
    alldat=[alldat;load([num2str(s),'_myfile_',num2str(r),'.mat'])];  % concatenate each 
  end
end

ADDENDUM

If don't have a huge number this shouldn't be too bad altho it's generally not "best practice" to dynamically grow arrays. Not sure w/ structures what happens if create an empty structure array vis a vis concatenation; never tested it.