finding unique rows with largest value in 3rd column
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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
Sean de Wolski
2013-12-19
So the order of the first two columns doesn't matter?
Mahi Nazir
2013-12-19
采纳的回答
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
Image Analyst
2013-12-19
He only wanted one row with 1 in the first column not two, and that would be the row that had 9 in column 3, not 8 because 9 is larger than 8.
Mahi Nazir
2013-12-19
Sean de Wolski
2013-12-19
Even less work:
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(x(:,1));
v = accumarray(idx,x(:,3),[],@max);
vv = [uv v]
vv =
1 9
2 8
4 2
Mahi Nazir
2013-12-19
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)
更多回答（1 个）
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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