How do I create a n by n matrix, randomly filled with only k specific values ; m1,m2,m3..mk where m1, m2, m3..mk are specified

Example

Say I want a 3 by 5 matrix filled randomly with only 2 particular values 2 and 6

A=

2 6 2 2 6; 6 2 6 6 2; 2 2 6 2 2;

I'm thinking of using a function like Rand and combine it with a round function, any tips/solutions are much appreciated!

-Tarun

Answer 1

[Image Analyst]

Try this:

myNumbers = [2.3, pi] % Whatever
% Find out how many unique numbers there are.
numNumbers = length(unique(myNumbers))
% Create a labeled 3-by-5 matrix with values from 1 to numNumbers
m = randi(numNumbers, 3, 5)
% Now replace each integer label ID of m with the value from myNumbers
for k = 1 : numNumbers
  m(m == k) = myNumbers(k);
end
% Print to command window:
m

In the command window you'll see:

myNumbers =
          2.3       3.1416
numNumbers =
     2
m =
     1     2     1     2     2
     2     1     1     1     2
     1     2     1     1     2
m =
          2.3       3.1416          2.3       3.1416       3.1416
       3.1416          2.3          2.3          2.3       3.1416
          2.3       3.1416          2.3          2.3       3.1416

It's generalizable to any numbers you want to use, not just integers, and any number of rows and columns.

[Tarun Cousik]

That is so cool!Thanks,its much better than the way I did it.

My real objective was to create a 100 by 100 matrix filled with either 1s or -1s. I generated random values between 0 and 1, rounded them to closest integers i.e 0 and 1. Then I, replaced all 0s by -1. This would have not worked great for the question I asked.

Your solution is awesome, thanks a lot!

Thanks, Tarun

[Image Analyst]

That's far simpler. Simply use randi():

m = 2 * randi([0,1], 100) - 1

[James Tursa]

If you just want -1 or +1, then see this link:

http://www.mathworks.com/matlabcentral/answers/306783-a-matlab-code-of-getting-a-value-uniformly-at-random-from-a-the-set-1-1