# How can I use the data of a set of matrices labelled in order

4 views (last 30 days)
Christian on 10 Jul 2024
Edited: Matt J on 11 Jul 2024
Hi, I managed to open all files in a folder which leaves me with the matrices data_1, data_2, data_3 .....data_n.
Now I want to add one of the row from each of the n matrices into one single set of data but I don't know how i can address the matrix in a for loop.
for i=1:1:n
ag((((i-1)*n)+1):i*ni)=data'i';
end
Walter Roberson on 10 Jul 2024
files = dir('C:\Work\HumenTestsJune24\2023-Taifun-Sula\8-31\31\*.txt');
filenames = fullfile({files.folder}, {files.name});
for k = 1:length(files)
end
Christian on 11 Jul 2024
Edited: Christian on 11 Jul 2024
Dear Walter,
thank you, this worked perfectly. I can adress the cells and take it from there!

Matt J on 11 Jul 2024
Edited: Matt J on 11 Jul 2024
data_1=10;
data_2=20;
data_3=30;
data_4=40;
data_5=50;
Data=arrayfun(@(i)evalin('caller', "data_"+i), 1:5,'uni',0)
Data = 1x5 cell array
{[10]} {[20]} {[30]} {[40]} {[50]}
Stephen23 on 11 Jul 2024
Note that the EVALIN documentation states "In most cases, using the evalin function is also less efficient than using other MATLAB functions and language constructs, and the resulting code can be more difficult to read and debug. Consider using an alternative to evalin."
The simpler and much more efficient alternative is to use indexing.
Matt J on 11 Jul 2024
Edited: Matt J on 11 Jul 2024
The point of the answer is not to be efficient, however. It is to undo the damage and convert the data to a form where it can be indexed.

Stephen23 on 11 Jul 2024
Edited: Stephen23 on 11 Jul 2024
"Thank you also for pointing about about dynamic variables, but as a beginner I am lacking options."
It shows the recommended approach using indexing. You should use indexing. Indexing is simple, reliable, and efficient. Indexing is a MATLAB superpower!
READMATRIX would likely be a better choice than LOAD. You could also use the same structure returned by DIR:
S = dir('C:\Work\HumenTestsJune24\2023-Taifun-Sula\8-31\31\*.txt');
S = natsortfiles(S); % optional, see text below
for k = 1:numel(S)
F = fullfile(S(k).folder,S(k).name);
end
All of the imported filedata will be in the structure S. This has the benefit that the imported filedata are stored together with corresponding filenames in one array. You can trivially access it using indexing, for example the 2nd file:
S(2).name
S(2).data
If you expect the files to be processed in alphanumeric order (of their filenames) then you could download my function NATSORTFILES and use it to sort the directory S as shown:
** The MATLAB documentation contains a lot of information. The more you practice browsing it, the more you will be able to use it effectively!

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