MATLAB: Sorting specific rows with a specific column

sort

I would like to sort first 3 rows of a matrix A with column 2 and then next 3 rows without changing the first three rows again with column 2. eg, A = [1 6 50; 5 2 50; 7 1 50; 2 5 53; 5 1 53; 7 3 53] Later, with same logic, I would like to sort a matrix with 100 rows.

Best Answer

The question is not clear. What does "sort with column 2" mean? A guess:
A = [1 6 50; 5 2 50; 7 1 50; 2 5 53; 5 1 53; 7 3 53];
for k = 1:3:size(A, 1)
  [dummy, index] = sort(A(k:k+2, 2));
  A(k:k+2, :)    = A(index + k - 1, :);
end
Please check if this produces the wanted output. If so, explain, if you need more speed.
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