I'm trying to generate a randomly scattered but limited number of 1's in a matrix of zeros efficiently.
Say I have a 10x10 matrix of zeros (zeros(10)) and I want to randomly place ten 1's so it looks like:
0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 1 0 0 0 0
0 0 1 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 0
1 0 0 0 0 1 0 0 0 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 0 0 0 1 0 0
0 0 0 0 1 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0
How can I do this WITHOUT a for-loop and without manually plugging in each position (this example is a much smaller version of my real problem)?
My code so far:
% Generate zeros
M = zeros(10)
% Generate random indices
Rands = [randsample(10, 10) randsample(10, 10)]
Where the first column is intended to be the row indices and the second column the column indices.
Now I obviously can't just drop these indices into the row and column indices of M like this:
M(Rands(:,1), Rands(:,2)) = 1
How can I vecorise the changes to these random indices?
You can use randperm to randomly generate the linear indices to be filled with 1:
sz = [10 10]; % desired size
n = 10; % desired number of ones
M = zeros(sz);
M(randperm(prod(sz), n)) = 1;
Alternatively, you can use randperm and reshape in one line:
M = reshape(randperm(prod(sz))<=n, sz);