MATLAB: Convert vector into ‘matrix equivalent’

Question

I have a vector of binomially distributed random numbers from i = 0 to n eg R = [0 1 2 1 4]'

I want to convert this this into a matrix of dimensions length( R ) by n where each row contains either zeros or ones. The number of ones required in each row is taken from the equivalent value in R. Otherwise values are zero. I would like the position of the ones within each row to be random. For instance, if R above and n = 5 then one matrix would be S = [ 0 0 0 0 0; 0 0 1 0 0; 0 1 1 0 0; 0 0 1 0 0; 1 1 1 0 1]

In practice,R is large with 1e6 values so I need the operation to be as fast as possible.

Many thanks!

Answer 1

[~, permidx] = sort( rand(length(R), n), 2);
S = permidx <= repmat(R(:),1,n);