Matrix's and percents

How would I go about making a 10 by 10 matrix with only 1,2,and 3's. And having 20% be 1, 40% be 2 and 40% be 3's?

Answer 1

[Honglei Chen]

x = rand(10);
x1 = zeros(10);
x1(x<0.2) = 1;
x1(0.2<=x&x<0.6) = 2;
x1(x>=0.6) = 3;

or if you want precise 20%, 40% and 40%, you can do

x = zeros(10);
k = randperm(100);
x(k(1:20)) = 1;
x(k(21:60)) = 2;
x(k(61:100)) = 3;

[Image Analyst]

Does not guarantee the 20, 40, 40 percentages - just try it and see.

[Honglei Chen]

Yes, I realized it, so I updated the answer.

Answer 2

[Image Analyst]

Try this:

m = ones(10, 10) % Create 1's
% Need 40 2's
% Could set to 4 but let's make it more general
numberOf2s = 0.4 * numel(m); 
% Get their locations
locationOf2s = randperm(numel(m), numberOf2s);
% Assign them
m(locationOf2s) = 2
% Now need 40 threes, but not where there are already 1s or 2s.
% Could set to 40 but let's make it more general
numberOf3s = 0.4 * numel(m); 
% First find locations of 1s.  We need to replace some of them
linear1indexes = find(m == 1)
% Get 40 random locations from those
indexesOf3s = randperm(length(linear1indexes), numberOf3s)
% Initialze a logical index array.
locationOf3s = false(length(linear1indexes));
% Set the location where 3s will go to true.
locationOf3s(linear1indexes) = true;
% Set those locations = 3
m(locationOf3s) = 3