Finding maximum y value corresponding to same x values.
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I have a n by 2 array.
x y
1 5
1 7
1 9
2 8
2 22
2 11
5 5
5 10
5 20
I'd like to spit out an array of the max y coordinate that corresponds to each x coordinate. So I'd have:
1 9
2 22
5 20
Thanks for any help!
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Answers (3)
Sean de Wolski
on 21 Feb 2013
xy = [
1 5
1 7
1 9
2 8
2 22
2 11
5 5
5 10
5 20];
[uv,~,idx] = unique(xy(:,1)); %what do they correspond to?
xmax = accumarray(idx,xy(:,2),[],@max); %build matrix
[uv xmax]
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Azzi Abdelmalek
on 21 Feb 2013
Edited: Azzi Abdelmalek
on 22 Feb 2013
[a,b]=unique(x);
for jj=1:numel(a);
e(jj)=max(y(x==a(jj)));
end
result=[a e]
0 Comments
Shashank Prasanna
on 21 Feb 2013
Quickest way I can think of is using accumarray:
% let xy be your array
A = accumarray(xy(:,1), xy(:,2), [], @max)
[unique(xy(:,1)) A(A~=0)]
ans =
1 9
2 22
5 20
2 Comments
Sean de Wolski
on 22 Feb 2013
Edited: Sean de Wolski
on 22 Feb 2013
If you run the unique command first, you skip having to remove the zeros. With 1,2,5 whatever, with 1,2, 5000000 you run out of memory...
With my approach, you build a 1x3 vector regardless of the values, even if they're non-integer :)
Shashank Prasanna
on 22 Feb 2013
That's good to note! I didn't see your reply before i put mine in. Thanks for the tip!
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