MATLAB: Tricky matrix conversion question

MATLABtricky matrix conversion

Hey all,
I am trying to convert a matrix A into a new matrix B, by looking at each element in matrix A and whenever the next element (in a row) is different, make a pair and add it to the new matrix B. Also elements with number 0 should be ignored.
As an example: Suppose we have a matrix A, and we want the resulted matrix B.
A = [1 1 1 3 5      B = [1 3
     2 2 0 4 5           3 5
     2 2 0 0 5]          2 4
                         4 5
                         2 5]
This problem could be solved by using a for-loop over all elements in the matrix, however for computational time reasons i am looking for a faster way to convert this, any ideas are welcome 😀

Best Answer

Actually, it can be done fairly easily without a loop. Whether or not it's faster than Adam's loop, I haven't tested.
A = [1 1 1 3 5;2 2 0 4 5; 2 2 0 0 5];
rows = repmat(1:size(A, 1), size(A, 2), 1);
At = A';
mask = At ~= 0;
Anz = At(mask);
pair1 = diff(Anz) ~= 0 & ~diff(rows(mask));
B = [Anz(pair1), Anz([false; pair1])]
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