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

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Anna M 2019-6-24

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评论： Anna M 2019-7-2

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!

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Stephen23 2019-6-25

编辑：Stephen23 2019-6-25

"...assign it to a variable name, such as X1, X2,...,X24. How can I do this?"

Do NOT do this.

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

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

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

You should use indexing. Inexing is neat, easy to debug, and very efficient.

Anna M 2019-7-2

Thank you! I will definitely look into that.

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Answer 1

James Tursa 2019-6-24

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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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infinity 2019-6-25

Hello, Thank @James Tursa for mentioning this issuse of eval function.

I recommend @Anna M to refer these solutions.

Anna M 2019-7-2

Thank y'all for the help. It is appreciated

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Answer 2

infinity 2019-6-24

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在 MATLAB Online 中打开

Hello,

Here is an example that you can refer

for i = 1:24
v = genvarname(['X' num2str(i)]);
eval([v '= A(:,3*i);']);
end

where A is your matrix.

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Anna M 2019-7-2

Thank you so much!

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

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