Sort Matrix by rows

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Ege
Ege on 23 Oct 2014
Edited: Guillaume on 23 Oct 2014
I have a matrix which first row indicates index numbers and second indicated the data. For example it goes like this:
1 2 3 4 5 6
23 45 10 90 11 34
I want to sort these descending but I don't want to loose the corresponding index either.
4 2 6 1 5 3
90 45 34 23 11 10
I have a large amount of data so it needs to be efficient too. How can I do that?

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Accepted Answer

Julia
Julia on 23 Oct 2014
Edited: Julia on 23 Oct 2014
Hi,
A =
1 2 3 4 5 6
23 45 10 90 11 34
>> A=A'
A =
1 23
2 45
3 10
4 90
5 11
6 34
>> B=sortrows(A,-2)
B =
4 90
2 45
6 34
1 23
5 11
3 10
>> B=B'
B =
4 2 6 1 5 3
90 45 34 23 11 10
Or short:
B=(sortrows(A',-2))'
B =
4 2 6 1 5 3
90 45 34 23 11 10

More Answers (3)

Torsten
Torsten on 23 Oct 2014
B=(sortrows(A',-2))';
where A is your input matrix.
Best wishes
Torsten.
Geoff Hayes
Geoff Hayes on 23 Oct 2014
Ege - consider using sortrows to perform the above task
A = [1 2 3 4 5 6
23 45 10 90 11 34];
B = sortrows(A',-2)';
We transpose A so that we can sort on the second column. The negative indicates descending sort order. The result is then transposed to get the desired output as
B =
4 2 6 1 5 3
90 45 34 23 11 10
Guillaume
Guillaume on 23 Oct 2014
Edited: Guillaume on 23 Oct 2014
Transpose your matrix, use sortrows along the second column, transpose it back and flip it left to right to get descending order
m = [1 2 3 4 5 6
23 45 10 90 11 34];
fliplr(sortrows(m', 2)')

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