finding unique rows with largest value in 3rd column
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Mahi Nazir
le 19 Déc 2013
Modifié(e) : Muhammet Bozkaya
le 20 Nov 2017
Suppose I have a matrix
A=
1 2 3
1 3 8
2 1 3
2 1 5
2 2 8
1 2 9
4 3 2
I want to find a matrix which has unique first column and largest 3rd column.. So my resultant matrix should be
1 2 9
2 2 8
4 3 2
Any help will be highly appreciated!
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Réponse acceptée
Sean de Wolski
le 19 Déc 2013
Modifié(e) : Sean de Wolski
le 19 Déc 2013
Assuming that the order of the first two columns doesn't matter and that your expected matrix is missing [1 3 8]
Old/clarified in comments
x = [1 2 3
1 3 8
2 1 3
2 1 5
2 2 8
1 2 9
4 3 2];
[uv,~,idx] = unique(sort(x(:,[1 2]),2),'rows');
v = accumarray(idx,x(:,3),[],@max);
vv = [uv v]
vv =
1 2 9
1 3 8
2 2 8
3 4 2
5 commentaires
Sean de Wolski
le 19 Déc 2013
Well do you want the first occurrence of the second column or the maximum one? etc. I guess, how do you wish to pick the second value (e.g. 2 1 v. 2 2)
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Muhammet Bozkaya
le 20 Nov 2017
Modifié(e) : Muhammet Bozkaya
le 20 Nov 2017
Simple answer for this case.
First sort rows with ascending 1st column and descending 3rd column(column you want to get the max), then see take unique...
A=[1 2 3
1 3 8
2 1 3
2 1 5
2 2 8
1 2 9
4 3 2];
A=sortrows(A,[1 -3]);
[~,idx]=unique(A(:,1));
A=A(idx,:);
result: 1 2 9
2 2 8
4 3 2
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