How does this vector expanding work?

Good night, I'm trying to understand how a vector can expand to a matrix using a vector formed by ones. Here is the example I'm trying to understand:

xx = [1 2 3]; yy = xx(ones(3,1),:);

I don't know how the part of xx(ones(3,1),:) works, and it would be great if you could explain it to me. The result of this operations is a 3x3 matrix:

 1 2 3
 1 2 3
 1 2 3

Thank you!

Answer 1

[Sean de Wolski]

Think about it this way:

x = [1 2;3 4];

to index the first row of this, you would use:

x(1,:)

If you wanted to index the 2nd row then the first row:

x([2 1],:)

What you're doing above is essentially:

x([1 1 1],:)

[Daniel]

I've finally understood it! Thank you, it has been very useful!