From vector to matrix reshape every ith rows for each column

I have this vector:

   arr = [1; 2; 3; 1; 2; 3; 1; 2; 3; 1; 2; 3]

And would like to turn it into a 4x3 matrix looking like this:

    mat = [1 1 1;...
    2 2 2;...
    3 3 3;...
    1 1 1;...
    2 2 2;...
    3 3 3;...
    1 1 1;...
    2 2 2;...
    3 3 3;...
    1 1 1;...
    2 2 2;...
    3 3 3]

So far I achieved this by doing:

a1 = arr(1:3:end);
    a2 = arr(2:3:end);
    a3 = arr(3:3:end);
    mat = [a1 a2 a3];

Is there a more convenient way with for instance the

reshape

function?

[Stephen23]

"And would like to turn it into a 4x3 matrix looking like this"

But what you showed is a 12x3 matrix.

So which is correct: what you wrote (4x3) or what you showed us (12x3) ?

Answer 1

[madhan ravi]

use repmat() for copying

>> arr = [1; 2; 3; 1; 2; 3; 1; 2; 3; 1; 2; 3]
mat=repmat(arr,1,3)

arr =

     1
     2
     3
     1
     2
     3
     1
     2
     3
     1
     2
     3


mat =

     1     1     1
     2     2     2
     3     3     3
     1     1     1
     2     2     2
     3     3     3
     1     1     1
     2     2     2
     3     3     3
     1     1     1
     2     2     2
     3     3     3

>> 

Answer 2

[Stephen23]

>> mat = [arr,arr,arr]
mat =
   1   1   1
   2   2   2
   3   3   3
   1   1   1
   2   2   2
   3   3   3
   1   1   1
   2   2   2
   3   3   3
   1   1   1
   2   2   2
   3   3   3

Answer 3

[Guillaume]

If you want to achieve what your code does instead of the result you show (see Stephen's comment):

mat = reshape(arr, 3, []).'

Otherwise, use Madhan's or Stephen's answer.