load several (one after another ) .mat Files via a For-Loop Job

Question

Trier87 2013-1-17

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评论： Veena Chatti 2020-1-12

Hello, i have a Program that is in the Folder-Directory: Main. And i have some several numbered .mat-Files with the Variable Buff that are in the Folder Directory Main/Combination:

combinations_1.mat
combinations_2.mat
combinations_3.mat
...and so on

My Program should load the first combinations_1.mat and to something:

for I = 1:size(Buff,1) 
% calculate some stuff
end

After the Loop is done it should load combinations_2 and start the Loop again

My Idea is:

d = dir('*.mat');          % only looking for .mat-Files           
Number_mat = length(d);    % number of .mat-Files         
for i=1:Number                    
    load(['combinations_' num2str(i) '.mat']) 
end

But i no idea how i can this combine with the For-Loop. Hope everybody understand my aim, big thanks

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Answer 1

Sarah Wait Zaranek 2013-1-17

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编辑：Jan 2013-1-17

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Unless I am missing something, I think the easiest thing would be to do a nested for loop.

for ii = 1: Number
 load(['combinations_' num2str(ii) '.mat'])
    for jj  = 1:size(Buff,1) 
    % calculate some stuff
    end
end

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Veena Chatti 2020-1-3

编辑：Veena Chatti 2020-1-3

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Hi Sarah,

I also have a similar question. I am trying to subplot the same variable from each of N mat files in a folder. I tried a nested for loop and an if condition. Right now it puts the same variable in all rows (the first one it loads). But I think it might work if I could load each mat file sequentially and refer to the same subplot in the loop. Please could you think of some ways I could adapt my code to do this? I would greatly appreciate your tips! My current code is as follows:

%%
read_folder = '...';
write_folder = '...';
cd(read_folder);
files = dir('*.mat');
N=numel(files);
  
R_y = [array of numbers]';
A_y = [another array of numbers]';
figure;
fig = gcf;
for i = 1:N
       for j = 1:6 %will need to change this as per numel(files).
       load(files(i).name, 'R', 'A')
       [pathstr,name,ext] = fileparts(files(i).name);
            newFilename = fullfile(pathstr,name);
    
        subplot(N,2,j)
        
        if mod(j,2) == 0
            subplot(N,2,j);
                          
            plot(A_y, A);
                               
        else mod(j,2) == 1 ;
            
            subplot(N,2,j);
            
            plot(R_y, R);
            
        end
       end
            cd(write_folder);
            saveas(fig, Image_name, 'png');
            cd(read_folder);
   
    end

Thanks!

Image Analyst 2020-1-3

编辑：Image Analyst 2020-1-3

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I'd do

rows = ceil(sqrt(N*6));

outside the loop, then inside the loop do

subplot(rows, rows, (i-1)*6+j);

This will make a square matrix of plots and each plot will go into a separate, new plot in that matrix.

Veena Chatti 2020-1-12

Thanks for your suggestion. I will test it soon.

Someone from MATLAB, Pujitha Narra, posted an answer on the question I asked, their solution worked really well!

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Answer 2

Image Analyst 2013-1-17

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You can use dir() to get a list of the filenames. Then you should check that the variable is actually in the mat file. Try this. It's a fairly robust adaptation of code already in the FAQ.

myFolder = 'Main/combinations'; % May need to correct this.
if ~isdir(myFolder)
  errorMessage = sprintf('Error: The following folder does not exist:\n%s', myFolder);
  uiwait(warndlg(errorMessage));
  return;
end
filePattern = fullfile(myFolder, 'combinations*.mat');
matFiles = dir(filePattern);
for k = 1:length(matFiles)
  matFilename = fullfile(myFolder, matFiles(k).name)
  matData = load(matFilename); % Retrieves a structure.
  % See if Buff actually exists in the data structure.
  hasField = isfield(matData, 'Buff');
  if ~hasField
    % Alert user in popup window.
    warningMessage = sprintf('Buff is not in %s\n', matFilename);
    uiwait(warndlg(warningMessage));
    % It's not there, so skip the rest of the loop.
    continue; % Go to the next iteration.
  end
  % If you get to here, Buff existed in the file.
  Buff = matData.Buff; % Extract the Buff from the structure.
  for row = 1 : size(Buff,1)
    % Calculate some stuff
  end
end