Randomly assort variables into 3xN matrix

I need a 3xN matrix that for example:

1 2 3 4 ... 10 ... 20

x: .5 .5 .5 .5 .5 .1

y: constant

z: canstant

I have 3 values of x that need to be random every 10 columns so like .5 for 1:10 then .1 for 11:20, then maybe it goes back to .5 for 21:30, then to 1 for 31:40

Answer 1

[dpb]

V=[v1;v2;v3];       % a vector of the three possible values (set elsewhere somehow; not explained)
ix=randperm(3);     % the randomized permutation of the three
x=cell2mat(arrayfun(@(i) repmat(V(i),1,size(x,2)/10),ix,'uniformoutput',0));