relabel the elements in each column according to the magnitude of these elements in an array
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Hi, I have
a=[4 5;
5 1;
6 4;
7 7]
I want to relabel the elements in each column according to the magnitude of these elements in the column to become
a=[1 3;
2 1;
3 2;
4 4]
How can I do this? Thank you.
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Accepted Answer
Star Strider
on 5 Jun 2014
Edited: Star Strider
on 5 Jun 2014
This works:
a=[4 5; 5 1;6 4; 7 7]
[as,ai] = sort(a,1);
b = [ai(ai(:,1),1) ai(ai(:,2),2)]
produces:
b =
1 3
2 1
3 2
4 4
It sorts the first and second columns independently. Then, to get the column indices as you want them, it maps each set of column indices to its own sorted indices. A bit complicated to explain, but taking the reference to the columns of b apart and looking at its components will reveal how it works.
12 Comments
Star Strider
on 7 Jun 2014
My pleasure!
It’s an unusual enough request that it took some time to come up with solution. When I was Answering another Question involving unique, it occurred to me that the unique function actually does exactly what you want.
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