How can I rearrange the order of N matrix in Matlab?

Hello all,

I created N matrix on matlab. named:

matrix_001

matrix_002

matrix_003

...

matrixN-1; matrix_N.

I would like to write a code which reorder the matrix that the last one become the first etc...

So i will look like:

matrix_N becomes matrix_001

matrix_N-1 becomes matrix_002

...

matrix_002 becomes matrix_N-1

Matrix_001 becomes matrix_N

Can someone help me to do that please?

[Adam Danz]

Are these matrices stored in an array and you're trying to flip that array? Or are the matrices each stored as a variable and you're trying to change the variable name? If the latter is what you're trying to do, it doesn't sound like a good idea.

[Stephen23]

"I created N matrix on matlab. named:"

matrix_001
matrix_002
matrix_003

Numbered variables are a sign that you are doing something wrong. Bad data design (like numbering variables) forces beginners to write bad code. Do NOT do this.

Dynamically accessing variable names is one way that beginners force themselves into writing slow, complex, obfuscated, buggy code that is hard to debug. Read this to know why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Indexing is simple, neat, easy to debug, and very efficient (unlike what you are trying to do). You should use indexing, exactly as the MATLAB documentation recommends: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array."

source: https://www.mathworks.com/help/matlab/matlab_prog/string-evaluation.html

[Jonathan Demmer]

Sorry my mistake its not matrices, its different files containing matrices.

Regards

Answer 1

[Guillaume]

Read Stephen's comment and follow the links to understand why your original design is very flawed.

You want only one variable containing all the matrices. It can either be a cell array or an N-d matrix (where N is 1 dimension more than your current matrices). Either way, rearranging the order of the matrices becomes a one-liner:

%with a cell array
%c = {matrix_001, matrix_002, etc...};
newc = c(end:-1:1);

%with an N-d array
%m = cat(ndims(matrix_001)+1, matrix_001, matrix_002, ...);
newm = flip(m, ndims(m));

[Jonathan Demmer]

Thank you very much Guillaume.

Regards

[Jonathan Demmer]

Sorry it is not matrice, its files.... here is the script, I wrote to create the files (velocity):

file = 'VELOCITY_####.mat';
for it = 1:N;
    m = telstepr(m,it);
    file(15:18)=sprintf('%04.0f',it);
    % 
    U = griddata(m.XYZ(:,1),m.XYZ(:,2)',m.RESULT(:,1),xq,yq');
    V = griddata(m.XYZ(:,1),m.XYZ(:,2)',m.RESULT(:,2),xq,yq');
    H = griddata(m.XYZ(:,1),m.XYZ(:,2)',m.RESULT(:,3),xq,yq');
    save(file,'U','V','H');
end

Each velocity file contains three matrices (U,V and H).

I would like to change the name of the file i.e.

VELOCITY_0001 becomes VELOCITY_N

VELOCITY_0002 becomes VELOCITY_N-1

...

do I have to do what you said nefore and all add them in one variable? or should i just write a code tochange their name?

[Guillaume]

Note that instead of

file = 'VELOCITY_####.mat';
for %...
    %...
    file(15:18)=sprintf('%04.0f',it);
    %...
end

I would have written

fileformat = 'VELOCITY_%04d.mat';  %put the format here. I've also changed the format to something better
for %...
    %...
    file = sprintf(fileformat, it);
    %...
end

Yes, your question was badly phrased. Files and matrices are completely different things.

Why do you want to rename the files? Would it be simpler to create them with the correct name in the first place? You can use matlab to rename the files (matlab will delegate the actual renaming task to your OS) but to give you the code we need more details. Is it all the mat files in the same directory than need renaming? Is there any other mat files in that directory that follow a different naming convention and should be ignored?

Also, what are you going to do with these files afterward. Maybe it would be better to save everything in just one file.

[Jonathan Demmer]

Sorry again the question was badly phrase and please accept my apologies... :(

Each velocity file correspond to a time step of the model (the first velocity file correspond to the first time step etc...). The Telemac tool function I used, only read the model (created in Telemac) from the first time step to the last one, so when i use it to create the different velocity files, unfoirtunately it can not start from the end.This is the reason why i cant create them with the right name.

All the files are in the same directory indeed and there is no other .mat file in the directory.

Each file contained: 2 velocities matrices (U and V) and 1 depth matice, the model has been ran for two month with a time step of 30 min (= 2929 files with three matrices in each). The totality of these files are 2TB (really heavy). I used these files to run a particle tracking model (PTM) in the Irish Sea. They need to be all separate because i use them differently to study the tide impact on the particles dispersal i.e. the model sometimes starts at the timestep 600 and finish at 900 and sometimes it could be totally different. Since i started to work on this project, i studied where the particles would agglomerate from a certain source.

My idea today is to run the model but in a reverse mode i.e. we know where the particle agglomerate lets try to identify the source... for that i need to run the PTM backward.

We thought about it a lot with my supervisor and the best way to do it, with out writing a code too long and too complicated which will take ages to run is just to change the name of the files. However, i have no idea, how to do... Does it help?

Regards

[Guillaume]

This should do it. Note that is assumes that your file follow exactly the pattern you've detailed as I'm relying on the fact that with that pattern the alphabetic order of the file is the same as the numeric one.

With some more complex code, we could actually extract the numeric part of the file, I'm not doing that here

folder = 'C:\somewhere\some\folder';
tempname = '_temprename';  %can't rename in place, so move files in temp folder

tempfolder = fullfile(folder, tempname);
if ~exist(tempfolder, 'dir')
    mkdir(tempfolder);
else
    error('temporary renaming folder already exist. Aborting to avoid overwriting files');
end
filelist = dir(fullfile(folder, 'VELOCITY_*.mat'));    %get file list, orderered alphabetically
sourcefiles = {filelist.name};
destfiles = sourcefiles(end:-1:1);  %reverse order of files
cellfun(@movefile, fullfile(folder, sourcefiles), fullfile(tempfolder, destfiles));  %move and rename files in temp folder
movefile(fullfile(tempfolder, '*.*'), folder) %move renamed file back into original folder
rmdir(tempfolder);  %delete tempfolder

Note that the code is untested. Test it on a copy of your folder first, to make sure it works as desired and you don't loose any data.

[Jonathan Demmer]

Thank you very much for your answer its really helpful!!

Jonathan