How to take image from multi folders?

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D. Frank 2020-6-19

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评论： D. Frank 2020-6-22

Hi everybody

I have a few thousand folders, each folder contains 2 images with information in their name, i want to take randomly 1 image from each folder and put all the taken images into one new folder in desktop for further calculation, please help, thank you very much.

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Rik 2020-6-21

You mean you want to read an image? If you know the file names you can just use imread.

D. Frank 2020-6-22

Read image is the next step of computing these files, the main thing i want to do is taking 1 random image from each subfolder, and there are 2900 subfolders in 1 folder to add to path in matlab :((((((

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Monalisa Pal 2020-6-21

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编辑：Monalisa Pal 2020-6-22

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Hi,

'fetching a random image' part of the following code may help you

clearvars -global
clearvars
close all
clc
% creating destination folder
destination = 'destinationfolder';
mkdir(destination);
n_folders = 10; % say there are 10 folders
for i = 1:n_folders
    % fetching the contents of the folders
    foldername = ['folder_', num2str(i), '/'];
    path = [foldername, '*.png']; % or other imgfile extensions
    contents = dir(path); 
    
    % fetching a random image
    if numel(contents) < 2
        error([foldername, ' has only ', num2str(numel(contents)), ' image files']);
    end
    img_index = randi([1, numel(contents)], 1);
    disp(['From ', foldername, ' copying ', contents(img_index).name]);
    source = [foldername, contents(img_index).name];
    copyfile(source, destination);
end

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D. Frank 2020-6-22

编辑：D. Frank 2020-6-22

在 MATLAB Online 中打开

Thank you, Ms. Monalisa Pal and Mr. Walter Roberson, i belive that this one should be right

clear;
clearvars -global
clearvars
close all
clc
% creating destination folder
destination = 'Images_place';
mkdir(destination);
n_folders = 2950; % say there are 10 folders
exts = {'*.jpg', '*.gif', '*.png', '*.jpeg', '*.bmp'};
for i = 1:n_folders
    % fetching the contents of the folders
    foldername = ['Bigfolder', num2str(i), '/'];
    contents = cellfun(@(E) dir( fullfile(foldername, E) ), exts, 'uniform', 0);
    
    if isempty(contents)
        fprintf('caution: folder "%s" had no useable images\n', foldername);
        continue;
    end
    % fetching a random image
    img_index = randi([1, numel(contents)], 1);
    filename = fullfile(foldername, contents(img_index).name);
    copyfile(filename, destination);
end

But in the line

filename = fullfile(foldername, contents(img_index).name);

i got the error showed 'Dot indexing is not supported for variables of this type'

in the 'Bigfolder' i have 2950 subfolders and each subfolder has 2 images in the range from .jpg, .png and etc

Monalisa Pal 2020-6-22

在 MATLAB Online 中打开

Dear Mr. Frank,

I was not familiar with cellfun. Many thanks to Mr. Roberson for mentioning it. Since you mentioned that there are definitely 2 images in each folder, I had removed the check. But it definitely helps in debugging. Incorporating his suggestions here's how the code looks like:

clearvars -global
clearvars
close all
clc
% creating destination folder
destination = 'Images_place';
mkdir(destination);
n_folders = 2950; % say there are 2950 folders
exts = {'*.jpg', '*.gif', '*.png', '*.jpeg', '*.bmp'};
for i = 1:n_folders
    % fetching the contents of the folders
    foldername = ['Bigfolder', num2str(i), '/'];
    contents_parts = cellfun(@(E) dir( fullfile(foldername, E) ), exts, 'uniform', 0);
    contents = vertcat(contents_parts{:});    
    
    % fetching a random image
    if isempty(contents)
        fprintf(1, 'caution: folder "%s" had no useable images\n', foldername);
        continue;
    end
    img_index = randi([1, numel(contents)], 1);
    disp(['From ', foldername, ' copying ', contents(img_index).name]);
    filename = fullfile(foldername, contents(img_index).name);
    copyfile(filename, destination);
end

If this doesn't work, could you please share a screenshot of your command window and workspace? I might help in debugging the code futher.

Monalisa Pal 2020-6-22

在 MATLAB Online 中打开

Mr. Frank, I misunderstood the directory structure earlier. Lets see if this works.

clearvars -global
clearvars
close all
clc
% creating destination folder
destination = 'Images_place';
mkdir(destination);
folder = 'Bigfolder';
sub_folders = dir(folder);
%n_folders = 2950; % say there are 2950 folders
% n_folders = numel(sub_folders) - 2;
exts = {'*.jpg', '*.gif', '*.png', '*.jpeg', '*.bmp'};
for i = 3:numel(sub_folders)
    % fetching the contents of the folders
    foldername = ['Bigfolder/', sub_folders(i).name, '/'];
    contents_parts = cellfun(@(E) dir( fullfile(foldername, E) ), exts, 'uniform', 0);
    contents = vertcat(contents_parts{:});    
    
    % fetching a random image
    if isempty(contents)
        fprintf(1, 'caution: folder "%s" had no useable images\n', foldername);
        continue;
    end
    img_index = randi([1, numel(contents)], 1);
    disp(['From ', foldername, ' copying ', contents(img_index).name]);
    filename = fullfile(foldername, contents(img_index).name);
    copyfile(filename, destination);
end