How can I create cell arrays that are in sequential order?

I've written this code to iterate through a series of .jpg images in a folder in order to create greyscale images of each picture. However, the folder creates cell arrays that aren't in sequential order as in (1, 2, 3, 4...). Instead, it goes 136, 137, 138, 139, 14, 140, 141, 142, 143... and so forth. How can I create cell arrays that are in sequential order?

Answer 1

[the cyclist]

Instead of using num2str to create the string, use sprintf.

For example, you could ensure that the number 1 is expressed as 001, ensuring the ordering.

 sprintf('%03d',1)

ans =

    '001'

Answer 2

[Stephen23]

Two simple solutions:

1. add sufficient leading zeros to all of the numbers (then a character sort will give the correct order). The tricky thing here is knowing in advance how many is sufficient... this is a fragile solution because in the future a user might easily define more images but not change how many leading zeros there are.
2. download my FEX submission natsortfiles, which was written to solve exactly this problem. Use it simply like the examples in the help, the HTML documentation and the FEX description show. In your case you will want something like this:

D = uigetdir(...);
S = dir(fullfile(D,'*.jpg'));
C = natsortfiles({S.name});
N = numel(C);
I = cell(1,N);
for k = 1:N
    F = fullfile(D,C{k});
    I{k} = imread(F);
    ...
end

Note that it is recommended to use fullfile rather than concatenating strings together.