how to find maximum value in some specific group range of matrix

Question

abdul wahab aziz 2016-8-22

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评论： Andrei Bobrov 2016-8-23

i have a matrix

in which last column represents its count so i want a complete row which has max count answer for its 2nd and 3rd column grouping e.g 2 5 is a group here and max count is 6 so i must get 3 2 5 6., second group is 3 8 so for this i must get ans 2 3 8 6

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Answer 1

Andrei Bobrov 2016-8-22

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a = [3  2  5  6,
2  5  5,
2  5  3,
2  5  4,
2  5  1,
2  5  1,
2  5  3,
2  5  1,
3  8  6,
3  8  3,
3  8  3];
[~,~,c] = unique(a(:,2:3),'rows');
[ii] = accumarray(c,(1:size(a,1))',[],@(x)x(a(x,4)==max(a(x,4))));
out = a(ii,:);

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abdul wahab aziz 2016-8-23

THIS WORKS FINE BUT THE PROBLEM IS IF COUNT IS SAME IT CALLS FIRST MAX COUNTED ROW WHERE AS IT MUST REPEAT IF THERE IS SAME COUNT

Andrei Bobrov 2016-8-23

在 MATLAB Online 中打开

a = [3  2  5  6,
4  2  5  5,
5  2  5  3,
6  2  5  4,
7  2  5  1,
8  2  5  1,
9  2  5  3,
11  2  5  1,
2  3  8  6,
4  3  8  3,
12      3       8       6     % repeated max volue
5  3  8  3];
[~,~,c] = unique(a(:,2:3),'rows');
f = @(x){x(a(x,4)==max(a(x,4)))};
ii = accumarray(c,(1:size(a,1))',[],f);
out = a(cat(1,ii{:}),:);

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Answer 2

Azzi Abdelmalek 2016-8-22

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在 MATLAB Online 中打开

A=[3  2  5  6; 4  2  5  5; 5  2  5  3; 6  2  5  4; 7  2  5  1; 8  2  5  1; 9  2  5  3; 11  2  5  1; 2  3  8  6; 4  3  8  3; 5  3  8  3]
[ii,jj,kk]=unique(A(:,2:3),'rows','stable')
f=accumarray(kk,(1:numel(kk))',[],@(x) {A(x,:)})
for k=1:numel(f)
   [~,idx]=max(f{k}(:,4))
   out(k,:)=f{k}(idx,:)
end