How to access an individual column from data

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Betty 2017-11-28

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编辑： Stephen23 2017-11-28

Hi guys, this might be a simple question but i don't really know how to do it.

I have 10x8 matrix, and want to specify every column besides the first one as: x1,x2,x3,x4,x5,x6,x7. Like, x1 = [...], x2 =[...] etc. Until now i've done it manually by copy-paste the values, but i'm sure there is a much easier way.

Thanks, B!

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Stephen23 2017-11-28

"...i'm sure there is a much easier way."

Yes, there is: use indexing. Indexing is simple, neat, and very efficient. Do NOT magically create or access variable names in a loop:

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

Betty 2017-11-28

Can you give me an example of what will be easiest in my way?

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Answer 1

KSSV 2017-11-28

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在 MATLAB Online 中打开

It is not required to name each column by x1, x2....x10.....it is waste of time and not all necessary. Already you have all the data in a matrix form..this is sufficient.

A = rand(10,8) ;  % matrix
A(:,1)   % gives first column
A(:,7)   % gives seventh column 
A(:,end)  % gives last column ie eight

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Betty 2017-11-28

Why do you rand my matrix?

Stephen23 2017-11-28

编辑：Stephen23 2017-11-28

@Betty: KSSV did not "rand" your matrix. KSSV used rand as a substitute for the data that you did not give us. Without any data we cannot test code... so KSSV quite sensibly made some fake data using rand.

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Answer 2

Stephen23 2017-11-28

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编辑：Stephen23 2017-11-28

在 MATLAB Online 中打开

If mat is your matrix, then something like this:

mat = [...];
out = [...];
for k = 1:size(M,2)
    vec = mat(:,k);
    ... do whatever with vec
    out(k) = ... save the output
end

You will need to figure out the require size of the output matrix.

Note that basic MATLAB concepts, such as how to write loops and access data using indexing, are introduced in the introductory tutorials. These tutorials are highly recommended for all beginners:

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