Generating random ones and zeros controllably

I am making a simple game in MATLAB that requires ones and zeros to be generated in a 5x5 matrix. I want to prespecify the number of ones and let the program generate them randomly among the zeros in the matrix. I tried using the rand function but I couldn't find a way to do the above.

How can I generate the required matrix?

Answer 1

[Ced]

You can generate a vector ( or matrix if you like ) with the desired number of zeros and ones, and then permute them randomly using randperm.

Example for a 5x5 matrix:

N = 25;            % total number of elements
N_ones = 10;       % number of ones
v = zeros(N,1);
v(1:N_ones,1) = 1; % vector with desired entries

% Now, scramble the vector randomly and reshape to desired matrix
A = reshape(v(randperm(N)),5,5);

Answer 2

[dpb]

doc randperm  % note the second optional input...

Will leave as "exercise for the student" the actual application but is straightforward... :)

ADDENDUM

See some verbose ways so I'll throw in another...shorter is simply

N=5;                            % array size (dimension)
nOnes=10;                       % number of ones
a=zeros(N);                     % allocate the array
a(randperm(numel(a),nOnes))=1;  % set the one locations

Answer 3

[Charles Dunn]

Interesting question. There are probably a couple ways to do this. I would check out the randperm function.

sz = [5 5];
N = prod(sz);
n = 5;

vals = cat(2,ones(1,n),zeros(1,N - n));

result = reshape(vals(randperm(N)),sz);