MATLAB: For loop to extract every 3rd column out of matrix and assign as variable name

for loopiterationmatrix

I have a matrix that is 6001 x 72. I want to iterate through the matrix to extract every 3rd column, from 1:72, and assign it to a variable name, such as X1, X2,…,X24. How can I do this?

I have tried a for loop, but I keep getting error messages. I am a beginner in Matlab.

Thanks!

Best Answer

Do not do this! This will only lead to headaches downstream in your code for processing these variables (you will need to use more eval( ) statements etc) and will be a nightmare to debug. There are much better alternatives. E.g.,

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

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MATLAB: How to write a1=1;a2=2;a3=3; from A

Do NOT do this

This would actually be horribly slow, pointlessly complex, obfuscated, and very buggy way to write your code. You would make your code hard to debug, and a pain to work with. Read this to know why:

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

Using indexing would be simple, neat, and very efficient. You should use one array and indexing. Indexing is the solution you should be using, because it is the most efficient way to write MATLAB code, is simple, neat, and very easy to debug. Indexing is explained quite well in the MATLAB introductory tutorials, which are highly recommended for all beginners:

https://www.mathworks.com/help/matlab/getting-started-with-matlab.html

MATLAB: How to change struct name in a loop

Although there is a MATLAB function to do this, but it is a very bad practice to name your variables like this. It will make your code error prone and hard to debug. Therefore I am going to suggest the correct way to solve the problem. You should create a struct array and store the input number as a field of the struct. For example

for ii=1:10
  X = input('which individual? ');
  s(i).individualNumber = X;
  s(i).length = ...;
end

It will take 10 inputs from user and store them in struct array.

Best Answer

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MATLAB: How to change struct name in a loop

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