finding unique rows with largest value in 3rd column

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!

[Sean de Wolski]

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

[Mahi Nazir]

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.

Answer 1

[Sean de Wolski]

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

[Image Analyst]

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]

Yes you are right... I want only one row with 1 in first column

[Sean de Wolski]

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]

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]

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)

Answer 2

[Muhammet Bozkaya]

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