Removing duplicate rows (not "unique")
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I have a matrix with many (1e5+) rows and I want to remove both copies of all duplicate rows. Is there a fast way to do this? (This function needs to be run many times.)
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jgg
2016년 5월 4일
You can use the other calling methods to get replicate counts.
a = [1 2; 1 2; 2 3; 2 4; 2 5; 4 2; 4 2; 1 3; 1 3; 4 5];
[C,ia,ic] = unique(a,'rows');
[count key] = hist(ic,unique(ic));
Then you can just select the keys with non-unit counts and drop them.
채택된 답변
Roger Stafford
2016년 5월 5일
편집: Roger Stafford
2016년 5월 5일
Let A be your matrix.
[B,ix] = sortrows(A);
f = find(diff([false;all(diff(B,1,1)==0,2);false])~=0);
s = ones(length(f)/2,1);
f1 = f(1:2:end-1); f2 = f(2:2:end);
t = cumsum(accumarray([f1;f2+1],[s;-s],[size(B,1)+1,1]));
A(ix(t(1:end-1)>0),:) = []; % <-- Corrected
댓글 수: 6
saad sulaiman
2022년 11월 5일
greetings.
how could we apply this code to a mesh where we have coordinate points for each triangle, such that we remove the internal edges, or edges shared by two triangles?
thanks in advance.
추가 답변 (2개)
Azzi Abdelmalek
2016년 5월 4일
편집: Azzi Abdelmalek
2016년 5월 4일
A=randi(5,10^5,3);
tic
A=unique(A,'rows');
toc
The result
Elapsed time is 0.171778 seconds.
댓글 수: 3
Azzi Abdelmalek
2016년 5월 4일
편집: Azzi Abdelmalek
2016년 5월 4일
You said that unique function will leave a copy of duplicate rows. With this example, I show you that there is no duplicates rows stored! And also it doesn't take much time
Mitsu
2021년 8월 3일
I reckon your answer does not address OP's question because running the following:
A=[1 1 1;1 1 1;1 1 0];
tic
A=unique(A,'rows');
toc
Will yield:
A = 1 1 0
1 1 1
Therefore, A still contains one instance of each row that was duplicate. I believe Michael wanted all instances of each row that appears multiple times be removed.
GeeTwo
2022년 8월 16일
%Here's a much cleaner way to do it with 2019a or later!
[B,BG]=groupcounts(A);
A_reduced=BG(B==1); % or just A if you want the results in the same variable.
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