sort a matrix without using sort function

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John
John on 22 Jan 2013
Commented: Jan on 2 Oct 2017
how can I sort this matrix in descend order(only columns) without using sort function (my homework). for example: A= [
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9 ]
to
B=[
24 17 15 8 1
23 16 14 7 5
22 20 13 6 4
. . . . . .. . .
.. .. . .. . .. . ]
thanks
  3 Comments
John
John on 22 Jan 2013
thanks for your help ,I was able to get this script work. thank your very much.
Cedric
Cedric on 22 Jan 2013
+1 for the "homework" tag! If other students were as honest as that, they would get more of my time ;-)

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Answers (1)

Jan
Jan on 22 Jan 2013
Edited: Jan on 1 Oct 2017
Here a solution, which I would not submit except with a bold explanation:
B = zeros(size(A));
n = size(A, 2);
for iRow = 1:size(A, 1)
v = A(iRow, :);
while any(diff(v) > 0) % Test if sorted in descending order
v = v(randperm(n, n)); % If not, shuffle the elements randomly
end
B(iRow, :) = v;
end
This is based on the "infinite monkey" theorem: Even a randomly typing monkey will find the solution by accident. In consequence is not guaranteed to finish until your homework is due.
[EDITED] This is not a serious suggestion. If you deliver this as solution of a homework, you might get an extra point for a nerdy kind of humor, perhaps. Ask an internet search engine for better sorting algorithms.
  6 Comments
Pame
Pame on 2 Oct 2017
I like the insertion sort method, and i've got it to work for arrays, but not for matrixes.
Also currently trying to make a function which sorts matrixes in ascending order so that the lowest value element is in (1,1) and the highest value element is in the last row, last column.
Jan
Jan on 2 Oct 2017
But "matrices" are "arrays". Do you mean "vectors"?
Do you have a question? If so, I recommend to open a new thread.

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