How can I use a WHILE loop to pick an element in an array at random but not pick the same element more than once?

So far this is the code I have. Not too good at this, please keep codes simple (for, while loops, if statements, etc.)! Any help is appreciated!!

a=1;
while a~=10
    a=a+1;
    n=floor(10*rand+1);
    m=floor(10*rand+1);
    if n==n
        n=floor(10*rand+1);
        if m==m
            m=floor(10*rand+1);
        end
    end
    if board(n,m)~='1'
        board(n,m)='1';
        if board(n,m)~='1'
            board(n,m)='1';
        end        
    end
end

[Walter Roberson]

Why are you bothering to test if n==n and m==m ? The only time those can fail is if there is one or more nan values in n or m.

Now if you were to compare n to m...

[Raquel Preciado]

I thought by putting that within the while loop it will compare the last n value with the next one to make sure they dont repeat. I tried what you suggested but still getting the same result...

[Walter Roberson]

The first time through, there is no "last" value to compare against. And if there were, then you would have the risk of going back to the first element, such as [5 3 5] -- since the second 5 is not the same as the 3 previous, it would pass the test you were thinking of.

Answer 1

[Image Analyst]

I'm not sure what this uncommented code does, but presumably you do. All I can say is that if you want to pick a number from 1 to N but have no chance to repeat the number you need to make up a vector in advance and then pick the values in your loop. For example:

indexes = randperm(N); % Values from 1 to N all scrambled up.
while k < N
    thisNumber = indexes(k);
    % Now do whatever.....
    k = k + 1;
end

[Raquel Preciado]

Just to be clear, the matrix is a character array. Looks like:

I'm not dealing with numerical values.

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Answer 2

[Walter Roberson]

remaining = 1:10;
while ~isempty(remaining);
    idx = randi(length(remaining));
    n = remaining(idx);
    remaining(idx) = [];
    do something with n
end