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

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Jonathan Demmer 2019-3-19

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评论： Jonathan Demmer 2019-3-21

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?

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Stephen23 2019-3-19

"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 2019-3-19

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

Regards

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Answer 1

Guillaume 2019-3-19

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在 MATLAB Online 中打开

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));

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Jonathan Demmer 2019-3-19

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 2019-3-19

在 MATLAB Online 中打开

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 2019-3-21

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

Jonathan

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

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

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