Matlab Generating a Matrix with random elements

Question

How can I generate a Matrix with Boolean elements, but the sum of each row is equal to a certain constant number.

Answer 1

Lets say you want to have 20 columns (n=20) and your vector a contains the number of ones you want in each row:

n=20;
a= [5 6 1 9 4];
X= zeros(numel(a),n);
for k=1:numel(a)
    rand_order=randperm(n);
    row_entries=[ones(1,a(k)),zeros(1,n-a(k))];
    row_entries=row_entries(rand_order);
    X(k,:)=row_entries;
end
X=boolean(X);

What I do is generate me a random ordered index array rand_order then getting an array which contains the wanted number of ones filled with zero. Reorder those elements according to rand_order saving it and converting it to logical. And because of the use of a for loop rand_order is all the time computed again, so giving you different locations for your output:

 1     0     0     0     0     0     0     0     0     1     0     0     0     0     0     1     1     1     0     0
 0     0     0     1     0     0     0     1     1     0     1     0     0     0     0     0     1     1     0     0
 0     0     0     0     0     0     0     0     0     0     0     0     1     0     0     0     0     0     0     0
 1     0     0     1     0     1     1     0     1     0     0     1     1     0     0     0     1     1     0     0
 1     0     0     0     1     0     0     0     0     0     1     0     1     0     0     0     0     0     0     0

Answer 2

Is each row the same one number?

k = 5;
m = 10;
n = 10;

[~, I] = sort(rand(m,n), 2)    
M = I <= k

If you don't want the same number of 1s in each row, but rather have a vector that specifies per row how many 1s you want then you need to use bsxfun as well:

K = (1:10)';                        %//'
m = 10;
n = 10;

[~, I] = sort(rand(m,n), 2)    
M = bsxfun(@ge, K,I)