Is it possible to add row vectors into a matrix with a for loop?

Question

Stewart Tan 2019-8-19

0
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编辑： Chris 2019-8-19

I wonder if it's possible to add rows of a matrix one at a time with a for loop? Example, if i initialize a blank matrix:

mat = [0 0 0];

and i have some dummy samples:

sample1 = [1 2 3];
sample2 = [4 5 6];

and i want to do something like:

for i=1:2
    mat(i,:) = sample1;
end

so i would get:

mat = [1 2 3
       4 5 6]

as the output. The idea is that what if i can't predefine the size of the matrix beforehand and that I'm not entirely sure how many sample will be there until the process ends? Is it possible in matlab?

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Answer 1

Chris 2019-8-19

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https://ww2.mathworks.cn/matlabcentral/answers/476717-is-it-possible-to-add-row-vectors-into-a-matrix-with-a-for-loop#answer_388221

编辑：Chris 2019-8-19

在 MATLAB Online 中打开

A loop is not needed for your simple demo

>> mat = [sample1; sample2]
mat =
     1     2     3
     4     5     6

But yes you can in general append to existing matrixies, it is best to preallocate when you can.

>> aa = [];
>> for ii = 1:5
aa(:,ii) = rand(3,1);
end
>> aa
aa =
      0.90579      0.63236      0.54688      0.15761      0.48538
      0.12699      0.09754      0.95751      0.97059      0.80028
      0.91338       0.2785      0.96489      0.95717      0.14189
      