finding unique rows with largest value in 3rd column

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Mahi Nazir
Mahi Nazir 2013-12-19
编辑： Muhammet Bozkaya 2017-11-20
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!
  2 个评论
Mahi Nazir
Mahi Nazir 2013-12-19
No order doesn't matter. Actually second column is not useful. Uniqueness is based on first column and one having largest value of 3rd column is selected.

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Sean de Wolski
Sean de Wolski 2013-12-19
编辑：Sean de Wolski 2013-12-19
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 个评论
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Mahi Nazir
Mahi Nazir 2013-12-19
Thanks! I want to preserve the second column information, I need that in future... so I want all the 3 columns in my answer... I am sure it must be a small modification but I am unable to do it
Sean de Wolski
Sean de Wolski 2013-12-19
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
Muhammet Bozkaya 2017-11-20
编辑：Muhammet Bozkaya 2017-11-20
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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