concatenation of few matrix with a loop

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Joydeb Saha
Joydeb Saha 2020-10-7
评论： Joydeb Saha 2020-10-7
C{1} = [total1979_125_30];
C{2} = [total1980_125_30];
C{3} = [total1981_125_30];
C{4} = [total1982_125_30];
C{5} = [total1983_125_30];
...upto C{40} = [total2019_125_30];
just help me making the loop
So that I can use
A = cat(3,C{:});
M = mean(A,3);
  2 个评论
Stephen23
Stephen23 2020-10-7
The cause of your problem is that you put meta-data (e.g. dates) into variables names. Meta-data is data and belongs in variables, not in variable names. Once you have made that bad design decision, you force yourself into writing slow, complex, inefficient, obfuscated, buggy code to try and access those multiple data arrays:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
So far you have not told us the most important information: how did you get those arrays into the workspace? Did you write them all out by hand? My guess is that you used load in a loop, in which case you can fix the problem at its cause by loading into an output variable, e.g.:
N = the number of files
C = cell(1,N);
for k = 1:N
F = the k-th filename
S = load(F);
C(k) = struct2cell(S);
end
Note how this does not require evil eval anywhere. Once you tell us how you actually get those multiple variables into the workspace, someone can help you to import/create the data in a better way.

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Ameer Hamza
Ameer Hamza 2020-10-7
编辑：Ameer Hamza 2020-10-7
It was not a good idea to create a variable name like this: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval. Always use a cell array. Since you already created these, you can use the following loop to create the cell array now.
C = {};
vals = 1979:2019;
for i = 1:numel(vals)
[~, C{i}] = evalc(sprintf('total%d_125_30', vals(i)));
end
  12 个评论
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Ameer Hamza
Ameer Hamza 2020-10-7
Or the alternate solution suggested by Stephen to use a 3D array
C = cat(3, C{:});
M_new = C - M;
M_new will also be a 3D array.
Joydeb Saha
Joydeb Saha 2020-10-7
Yes, its working. Thank you very much for both your support.

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