How to force Matlab to read files in a folder serially?

Question

I have files in a folder that are numbered from writer_1 to writer_20. I wrote a code to read all the files and store them in cells. But the problem is

Answer 1

I don't know of any direct solutions to the problem you are having. I found a solution for a problem similar to yours, here

List = dir('*.png');
Name = {List.name};
S = sprintf('%s,', Name{:});    % '10.png,100.png,1000.png,20.png, ...'
D = sscanf(S, '%d.png,');       % [10; 100, 1000; 20; ...]
[sortedD, sortIndex] = sort(D); % Sort numerically
sortedName = Name(sortIndex);   % Apply sorting index to original names

Differences are:

1. You are dealing with directories instead of files
2. Your directories have other text in their names in addition to the numbers

Answer 2

Here is a slightly different way (edited to fix bug and implement suggestion of @Divakar to eliminate for loop)

folders = dir(Path_training);
folders(ismember( {folders.name}, {'.', '..'}) ) = [];

%// Get folder numbers as cell array of strings
folder_nums_cell = regexp({folders.name}, '\d*', 'match');

%// Convert cell array to vector of numbers
folder_nums = str2double(vertcat(folder_nums_cell{:}));

%// Sort original folder array
[~,inds] = sort(folder_nums);
folders = folders(inds);

Answer 3

Stealing a bit from DavidS and with the assumption that your folders all are of the form "writer_XX" with XX being digits.

folders = dir([pwd '\temp']);
folders(ismember( {folders.name}, {'.', '..'}) ) = [];

% extract numbers from cell array
foldersNumCell = regexp({folders.name}, '\d*', 'match');

% convert from cell array of strings to double
foldersNumber = str2double(foldersNumCell);

% get sort order
[garbage,sortI] = sort(foldersNumber);

% rearrange the structure
folders = folders(sortI);

The advantage of this is that it avoids a for loop. In reality it only makes a difference though if you have tens of thousands for folders. (I created 50,000 folders labeled 'writer_1' to 'writer_50000'. The difference in execution time was about 1.2 seconds.

Answer 4

Approach #1

%// From your code
folders = dir(Path_training);
folders(ismember( {folders.name}, {'.', '..'}) ) = []

%// Convert folders struct to a cell array with all of the data from dir
folders_cellarr = struct2cell(folders)

%// Get filenames
fn = folders_cellarr(1,:)

%// Get numeral part and sorted indices
num=str2double(cellfun(@(x) strjoin(regexp(x,['\d'],'match'),''), fn(:),'uni',0))
[~,ind] = sort(num)

%// Re-arrange folders based on the sorted indices
folders = folders(ind)

Approach #2

If you would like to avoid struct2cell, here's an alternative approach -

%// Get filenames
fn = cellstr(ls(Path_training))
fn(ismember(fn,{'.', '..'}))=[]

%// Get numeral part and sorted indices
num=str2double(cellfun(@(x) strjoin(regexp(x,['\d'],'match'),''), fn(:),'uni',0))
[~,ind] = sort(num)

%// List directory and re-arrange the elements based on the sorted indices
folders = dir(Path_training);
folders(ismember( {folders.name}, {'.', '..'}) ) = []
folders = folders(ind)

Please note that strjoin is a recent addition to MATLAB Toolbox. So, if you are on an older version of MATLAB, here's the source code link from MATLAB File-exchange.