shuffle blocks of elements in vector?

i have for example the following vector:

v = [1;2;3;4;5;6;7;8;9;10;11;12]

now i would like to cut them into blocks of 3 elements in a row and shuffle these blocks. the end result could look like this:

v_shuffled = [1;2;3;10;11;12;7;8;9;4;5;6]

my idea is to somehow store each block as a row vector in a matrix, shuffle these rows and then build a vector out of the shuffled matrix rows. this is what i have so far (code doesnt work)

for i=1:(length(v))/4
    u(i,1)=v(4*i);
    u(i,2)=v(4*i+1);
    u(i,3)=v(4*i+2);
    u(i,4)=v(4*i+3);
end

s = u(randperm(size(u,3)),:)

for i=1:length(v)/4
    h(4*i,1)=s(i,1);
    h(4*i+1,1)=s(i,2);
    h(4*i+2,1)=s(i,3);
    h(4*i+3,1)=s(i,4);
end

any ideas?

Answer 1

[Roger Stafford]

v = reshape(v,[],3);
v = reshape(v(randperm(size(v,1)),:),[],1);