Error using subsindex Function 'subsindex' is not defined for values of class 'struct'.

 clc; clear all;  close all;
 image_path = '/media/wangxiao/Elements/image_segment_backup/';
 savePath = '/media/wangxiao/Seagate/wangxiao/additional_data/';

 threshold  = ;

 first_files = dir(image_path);

 for i = :length(first_files)
     sec_file_name = first_files(i).name;
     sec_path = [image_path, sec_file_name, '/'];
     sec_files = dir(sec_path);
     disp(['process the: ', sec_file_name, '---', num2str(i-), '/', num2str(length(first_files)-),' waiting . . . ']);

     for j = :length(sec_files)
         third_file_name = sec_files(j).name;
         third_path = [sec_path, third_file_name, '/'];
         third_files = dir(third_path);
         disp(['     process the: ', third_file_name, '---', num2str(j-), '/', num2str(length(sec_files)-),'  . . . ']);

         for k = :length(third_files)
             fourth_files_name = third_files(k).name;
             fourth_path = [third_path, fourth_files_name, '/'];
             fourth_files = dir(fourth_path);
             disp(['         process the: ', fourth_files_name, '---', num2str(k-), '/', num2str(length(third_files)-),'  . . . ']);

             for ii = :length(fourth_files)
                 fifth_file_name = fourth_files(ii).name;
                 fifth_path = [fourth_path, fifth_file_name, '/'];
                 fifth_files = dir(fifth_path);
                 disp(['               process the: ', fifth_file_name, '---', num2str(ii-), '/', num2str(length(fourth_files)-),'  . . . ']);

                 for jj = :length(fifth_files)
                     six_file_name = fifth_files(jj).name;
                     six_path = [fifth_path, six_file_name, '/'];
                     six_files = dir([six_path, '*.jpg']);
 %                     disp(['                   process the: ', six_file_name, '---', num2str(jj-), '/', num2str(length(fifth_files)-), '  . . . ']);

                     for kk = :length(six_files)
                         seven_file_name = six_files(kk).name;
                         image = imread([six_path, seven_file_name]);

                         imshow(image);

                         [width, length, channel] = size(image);
                         %   disp(sec_file_name);
                         %   disp(third_file_name);
                         %   disp(fourth_files_name);
                         %   disp(fifth_file_name);
                         %   disp(six_file_name);
                         %   disp(seven_file_name);
                         resolution = width * length ;

                         if (resolution > threshold)
                             imwrite(image, [savePath, seven_file_name]);
                         end

                     end

                 end

             end

         end

     end

 end

Error using subsindex
Function 'subsindex' is not defined for values of class 'struct'.

Error in pre_deal_additional_data (line 39)
                    for kk = 1:length(six_files)

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fuck the error and  the answer is :

 clc; clear all;  close all;
 image_path = '/media/wangxiao/Elements/image_segment_backup/';
 savePath = '/media/wangxiao/Seagate/wangxiao/additional_data/';

 threshold_self  = ;

 first_files = dir(image_path);

 for i = :size(first_files, )
     sec_file_name = first_files(i).name;
     sec_path = [image_path, sec_file_name, '/'];
     sec_files = dir(sec_path);
     disp(['process the: ', sec_file_name, '---', num2str(i-), '/', num2str(length(first_files)-),' waiting . . . ']);

     for j = : size(sec_files, )
         third_file_name = sec_files(j).name;
         third_path = [sec_path, third_file_name, '/'];
         third_files = dir(third_path);
 %         disp(['     process the: ', third_file_name, '---', num2str(j-), '/', num2str(length(sec_files)-),'  . . . ']);

         for k = : size(third_files, )
             fourth_files_name = third_files(k).name;
             fourth_path = [third_path, fourth_files_name, '/'];
             fourth_files = dir(fourth_path);
 %             disp(['         process the: ', fourth_files_name, '---', num2str(k-), '/', num2str(length(third_files)-),'  . . . ']);

             for ii = : size(fourth_files, )
                 fifth_file_name = fourth_files(ii).name;
                 fifth_path = [fourth_path, fifth_file_name, '/'];
                 fifth_files = dir(fifth_path);
 %                 disp(['               process the: ', fifth_file_name, '---', num2str(ii-), '/', num2str(length(fourth_files)-),'  . . . ']);

                 for jj = :  size(fifth_files, )
                     six_file_name = fifth_files(jj).name;
                     six_path = [fifth_path, six_file_name, '/'];
                     six_files = dir([six_path, '*.jpg']);
 %                     disp(['                   process the: ', six_file_name, '---', num2str(jj-), '/', num2str(length(fifth_files)-), '  . . . ']);

                     for kk = : size(six_files, )
                         seven_file_name = six_files(kk).name;
                         image = imread([six_path, seven_file_name]);

 %                         imshow(image);

                         [width, length, channel] = size(image);

                         resolution_self = width * length ;

                         if (resolution_self > threshold_self)
                             imwrite(image, [savePath, seven_file_name]);
                         end

                     end

                 end

             end

         end

     end

 end