Select specified (max) values

Dear all, I've a matrix, e.g.:

A = [2 1 1 1440 62 2 6 8; 2 2 1 1882 65 2 7 8; 3 1 1 820 51 2 5 8; 3 2 1 1435 65 2 6 8; 3 3 1 1608 67 2 6 8; 9 1 1 394 38 1 2 8;9 2 1 2198 93 2 9 8; 9 2 2 2198 91 2 12 8; 9 2 3 2198 92 2 16 8; 9 3 1 2994 122 1 7 8; 9 3 2 2994 125 1 10 8; 9 3 3 2994 126 1 14 8];

For each row with the same value in the 1st and 2nd column, I've to take only the row where the 3th column is the maximum. I would, as result, a matrix like this:

B = [2 1 1 1440 62 2 6 8; 2 2 1 1882 65 2 7 8; 3 1 1 820 51 2 5 8; 3 2 1 1435 65 2 6 8; 3 3 1 1608 67 2 6 8; 9 1 1 394 38 1 2 8; 9 2 3 2198 92 2 16 8; 9 3 3 2994 126 1 14 8];

[key, ~, index] = unique(A(:,[1 2]),'stable','rows');
x = accumarray(index, A(:,3), [], @max);

...and I'm blocked here!

Answer 1

[Jan]

You can start with sorting the array according to the first 3 columns. Then take the rows which contain a change in the 1st or 2nd column, and the last row:

S     = sortrows(A, 1:3);                       % Largest 3rd col to bottom
Index = [diff(S(:, 1)) | diff(S(:, 2)); true];  % 1st or 2nd col changes
B     = A(Index, :)                             % Extract result