Sorting specific rows with a specific column

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.

Answer 1

[Jan]

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.

[Pushkar Mahajan]

Thanks Jan for the answer. You guessed it right. Final A should be, A = [7 1 50; 5 2 50; 1 6 50; 5 1 53; 7 3 53; 2 5 53] Would you please tell which website or book is useful in learning advanced things in Matlab like this?

[Jan]

I think the best web source for such questions is: https://www.mathworks.com/matlabcentral/answers/ :-)

After reading the Getting Started chapters of the documentation and seeing Matlab's Onramp, it helps do discuss such questions in the forum until you get familar with creating efficient algorithms. See also: https://www.mathworks.com/matlabcentral/answers/8026-best-way-s-to-master-matlab

[Pushkar Mahajan]

Thanks Jan. I will go through the links.