# Specialized sorting of array while preserving order

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Zaza el 21 de Nov. de 2012
how can i sort an array (of even number of elements) so the elements on the left side are smaller than the elements on the right side but without changing the original order of the elements in the array?
for example:
a = [19 21 12 -15 18 1 22 11];
r = [12 -15 1 11 19 21 18 22];
12 is prior to -15 in the original array and so it is in the result.
another example:
a = [8 4 2 6 3 1 9 10];
r = [ 4 2 3 1 8 6 9 10];
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Thomas el 21 de Nov. de 2012
Editada: Thomas el 21 de Nov. de 2012
Why is 12 first. The results seems to be random.
but 4 is larger than 2..

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Matt Fig el 21 de Nov. de 2012
Editada: Matt Fig el 21 de Nov. de 2012
a = [19 21 12 -15 18 1 22 11];
% Now the method:
L = length(a)/2;
[~,J] = sort(a); % For older MATLAB vers,[J,J] = sort(a);
[~,J] = sort(J);
r = [a(J<=L) a(J>L)]
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Zaza el 21 de Nov. de 2012
i read the help of sort but i still don't feel comfortable with that...
can you give me please a simple step-by-step ex.? it would be very helpful for me...
Matt Fig el 21 de Nov. de 2012
Editada: Matt Fig el 21 de Nov. de 2012
Zaza, it seems you already have a step-by-step example! Perhaps this will help. Here is another (preferable) way of solving the problem:
L = length(a)/2;
[~,J] = sort(a);
J(J) = 1:L*2;
r = [a(J<=L) a(J>L)]
Now have a look at Loren's blog entry on this method:

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