Dot indexing is not supported for variables of this type.

clear all
clc

sad = dir('D:\Project\DB1\test\');  % Returns both folders and files 
cell_array_of_folder_names = {sad([sad.isdir]).name};  % Select folder names 
cell_array_of_folder_names( strncmp( cell_array_of_folder_names, ".", 1 ) ) = []; % Remove '.' and '..' 
sorted_cell_array_of_folder_names = sort_nat( cell_array_of_folder_names );
%----------------

[mp1, np] = size(sorted_cell_array_of_folder_names); % compute size = number of subfolders & files & . & ..
csf1=0; % counter of JUST subfolders found in PF
t=1;
for i=1:mp1
%% keep only folders:
P = strfind(sorted_cell_array_of_folder_names(i).name,'.');
if isempty(strfind(sorted_cell_array_of_folder_names(i).name,'.'))
csf1 = csf1 +1; % one sub folder found
SFN = sorted_cell_array_of_folder_names(i).name ;% extract his name
tifList = ls(sprintf('%s%s%s%s',PF,SFN,'\','*.tif')); % list all jpg files
[ms1, ns] = size(tifList); % ms = number of image files found

%% Processing for each tif file:

for j=1:ms1
tifFileName = tifList(j,:); % extract name of tif file
IM=imread([PF SFN '\' tifFileName]);
%t=1;
%for i=1:csf1
 % for j=1:ms1
         Group_Test1(t)={i-2};
        t=t+1;
end
end
PF_SFN_imgName = sprintf('%s%s%s',PF,SFN,'\',tifFileName);

end
save('Group_Test','Group_Test1');
%----------------------

Dot indexing is not supported for variables of this type.

Error in Untitled2 (line 15)

P = strfind(sorted_cell_array_of_folder_names(i).name,'.');

>>

Answer 1

[Jan]

Replace:

strfind(sorted_cell_array_of_folder_names(i).name,'.');
% by
strfind(sorted_cell_array_of_folder_names{i},'.');

The name of the variable is cruel: "sorted_cell_array_of_folder_names". But it implies, that the variable is a cell array. So getting the field "name" is not working.

Your code can be simplified:

• Omit the brute "clear all". It removes all loaded functions from the memory. The reloading from the slow disk wastes time without any benefit.
• "folder_names" is a nice name, while "cell_array_of_folder_names" impedes reading the code.
• contains and startsWith are useful. Compare:

cell_array_of_folder_names( strncmp( cell_array_of_folder_names, ".", 1 ) ) = [];

with

folder_names(startsWith(folder_names, ".")) = [];

and

P = strfind(sorted_cell_array_of_folder_names(i).name,'.');
if isempty(strfind(sorted_cell_array_of_folder_names(i).name,'.'))

with

P = contains(folder_names{i}, '.');
if ~P

• This is cruel:

tifList = ls(sprintf('%s%s%s%s',PF,SFN,'\','*.tif')); % list all jpg files
[ms1, ns] = size(tifList);

Creating a char output only to count the lines is very indirect. Nicer:

tifList = dir(fullfile(PF, SFN, '*.tif'));
ms1     = numel(tifList);

• fullfile cares for the proper file separators.

[sun rise]

clc

sad = dir('D:\Project\DB1\test\');  % Returns both folders and files 
cell_array_of_folder_names = {sad([sad.isdir]).name};  % Select folder names 
cell_array_of_folder_names(startsWith(folder_names, ".")) = []; % Remove '.' and '..' 
folder_names = sort_nat( cell_array_of_folder_names );
%----------------

[mp1, np] = size(folder_names); % compute size = number of subfolders & files & . & ..
csf1=0; % counter of JUST subfolders found in PF
t=1;
for i=1:mp1
%% keep only folders:
P = contains(folder_names{i}, '.');
if ~P
csf1 = csf1 +1; % one sub folder found
SFN = folder_names{i} ;% extract his name
tifList = dir(fullfile( SFN, '*.tif')); % list all jpg files
ms1     = numel(tifList);% ms = number of image files found

%% Processing for each tif file:

for j=1:ms1
tifFileName = tifList(j,:); % extract name of tif file
IM=imread([ SFN '\' tifFileName]);
%t=1;
%for i=1:csf1
 % for j=1:ms1
         Group_Test1(t)={i-2};
        t=t+1;
end
end
%PF_SFN_imgName = sprintf('%s%s%s',PF,SFN,'\',tifFileName);

end
save('Group_Test','Group_Test1');
%----------------------

Error using save

Variable 'Group_Test1' not found.

Error in Untitled2 (line 36)

save('Group_Test','Group_Test1');

>>

[Jan]

After

tifList = dir(fullfile( SFN, '*.tif'))

tifList ius a struct. Then this must fail:

tifFileName = tifList(j,:); % extract name of tif file
IM=imread([ SFN '\' tifFileName])

Obviously the inner loop does not run at all.

Maybe this is the problem:

cell_array_of_folder_names = {sad([sad.isdir]).name};  % Select folder names 
cell_array_of_folder_names(startsWith(folder_names, ".")) = [];

I assume you mean:

folder_names = {sad([sad.isdir]).name};  % Select folder names 
folder_names(startsWith(folder_names, ".")) = [];

As far as I understand, the output Group_Test1 should be a cell array, which contains an index of the parent folder of each TIF file? This index should start at -1? Then:

tifList    = dir('D:\Project\DB1\test\**\*.tif');  % **: recursively
FolderName = {tifList.folder};
[~, ~, Index] = unqiue(FolderName, 'stable');
Group_Test1 = num2cell(Index - 2);
save('Group_Test', 'Group_Test1');

[sun rise]

tifList must be ordered using the sort_nat function

[Jan]

Then replace

FolderName = {tifList.folder};

by

FolderName = sort_nat({tifList.folder});

Answer 2

[Image Analyst]

I answered in your other question: https://www.mathworks.com/matlabcentral/answers/804541-variable-group_test1-not-found#comment_1477145