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

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?

Answer 1

[Chris]

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
      

Note you have to define aa first. Also you need to append with consistent row/column lengths.

Edit: to prevent some future problems you might want to read:

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