finding unique rows with largest value in 3rd column

Question

Mahi Nazir 2013-12-19

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https://ww2.mathworks.cn/matlabcentral/answers/110231-finding-unique-rows-with-largest-value-in-3rd-column

编辑： Muhammet Bozkaya 2017-11-20

采纳的回答： Sean de Wolski

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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Sean de Wolski 2013-12-19

So the order of the first two columns doesn't matter?

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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Answer 1

Sean de Wolski 2013-12-19

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https://ww2.mathworks.cn/matlabcentral/answers/110231-finding-unique-rows-with-largest-value-in-3rd-column#answer_118862

编辑：Sean de Wolski 2013-12-19

在 MATLAB Online 中打开

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

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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 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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Answer 2

Muhammet Bozkaya 2017-11-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/110231-finding-unique-rows-with-largest-value-in-3rd-column#answer_292064

编辑：Muhammet Bozkaya 2017-11-20

在 MATLAB Online 中打开

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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