Sorting a Matrix using Indices from another matrix !
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Dimitris M
le 13 Sep 2013
Commenté : Aaron Thode
le 31 Juil 2018
Hello
I have a pretty simple question !
I have a matrix A (lets assume has a size 5 x 5) and I have another matrix of same size (5 x 5) called IDX that contains the values for sorting A in a colum-wise manner.
So how can I easily sort each column of A using matrix IDX without using a for loop or extracting each column of IDX as an individual vector ?
Thank you in advance !
2 commentaires
the cyclist
le 13 Sep 2013
This would be much easier to answer if you gave examples of the two matrices, and the expected result.
Réponse acceptée
Azzi Abdelmalek
le 13 Sep 2013
[m,n]=size(A);
A=A(sub2ind([m n],idx,repmat(1:n,m,1)))
5 commentaires
Azzi Abdelmalek
le 13 Sep 2013
idx =[4 1 6;5 2 5;6 3 4;3 6 3;2 5 2;1 4 1];
A = [1:6;7:12;13:18]';
idx1=idx % indicate line index
4 1 6
5 2 5
6 3 4
3 6 3
2 5 2
1 4 1
[m,n]=size(A);
idx2=repmat(1:n,m,1) %indicate column index
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
1 2 3
idx=sub2ind([m n],idx1,idx2) % to get linear index
4 7 18
5 8 17
6 9 16
3 12 15
2 11 14
1 10 13
A=A(idx)
Plus de réponses (2)
Image Analyst
le 13 Sep 2013
Try this:
% Create random sample data so it will be easy
% for us to see if the sorting worked.
A = randi(9, [6,3])
IDX = [4 5 6 3 2 1;
1 2 3 6 5 4;
6 5 4 3 2 1]'
[rows, columns] = size(A)
% Sort columns of A according to the same column of IDX
for col = 1 : columns
A(:,col) = A(IDX(:,col), col);
end
% Print out to command window.
A
In the command window:
A =
7 7 7
3 8 7
9 2 3
1 5 7
4 5 6
4 6 2
IDX =
4 1 6
5 2 5
6 3 4
3 6 3
2 5 2
1 4 1
rows =
6
columns =
3
A =
1 7 2
4 8 6
4 2 7
9 6 3
3 5 7
7 5 7
0 commentaires
Azzi Abdelmalek
le 13 Sep 2013
Modifié(e) : Azzi Abdelmalek
le 13 Sep 2013
Edit2
A = [1 1 1 0 0 0; 0 0 0 1 1 1; 0 1 0 1 0 1]'
idx= [4 5 6 3 2 1; 1 2 3 6 5 4; 6 5 4 3 2 1]'
[m,n]=size(A);
idx=bsxfun(@plus,idx,(0:m:(n-1)*m))
A=A(idx)
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