MATLAB: Count how many times a number appears in a matrix and assign that increasing value to a new matrix

countindexingmatrix

I have a 32 x 6 matrix consisting of repeats of 1-16 in each column in a specific order, e.g., :
    X = [6  1  1  8  16  1
        2  16  6  6  9  8
        7  9  10  13  1  16
        15  5  3  6  3  11
        9  3  13  1  7  12
        10  11  8  7  5  7
         etc etc];
So given this set up, each instance of 1 – 16 will appear 12 times, twice in each column. What I need to do is create another matrix of the same size, indexing for each number where those repeats are occurring. So for example, if a column looked like this:
        1
        3
        3
        2
        1
it would return:
        1
        1
        2 (the second time 3 is appearing)
        1
        2 (the second time 1 is appearing)
I was thinking about using some kind of count function for each number and then perhaps applying a multiplication to it? Would be fine if these had to be separate matrices for each of the 16 numbers if that makes it any simpler. Any suggestions?

Best Answer

out = ones(size(X));
for j1 = 1:size(X,2)
    [u,i1] = unique(X(:,j1));
    id = i1(histc(X(:,j1),u) > 1);
    out(id,j1) =  out(id,j1) + 1;
end
or
out = zeros(size(X));
for j1 = 1:size(X,2)
    b = unique(X(:,j1));
    for jj = 1:numel(b)
        t = abs(X(:,j1) - b(jj)) < eps(100);
        out(t,j1) = 1:nnz(t);
    end
end
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