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

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Anna M on 24 Jun 2019
Commented: Anna M on 2 Jul 2019
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!

Stephen Cobeldick on 25 Jun 2019
"...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:
You should use indexing. Inexing is neat, easy to debug, and very efficient.
Anna M on 2 Jul 2019
Thank you! I will definitely look into that.

James Tursa on 24 Jun 2019
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.,

infinity on 25 Jun 2019
Hello, Thank @James Tursa for mentioning this issuse of eval function.
I recommend @Anna M to refer these solutions.
Anna M on 2 Jul 2019
Thank y'all for the help. It is appreciated

### More Answers (1)

infinity on 24 Jun 2019
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.

#### 1 Comment

Anna M on 2 Jul 2019
Thank you so much!