how to velocize it (avoid loop is possible)

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Luca Re
Luca Re 2024-2-3
评论： Matt J 2024-2-4
Ran in:
E=[0 5 6 9 2;0 0 1 3 1;0 5 4 2 4]'
E = 5×3
0 0 0 5 0 5 6 1 4 9 3 2 2 1 4
filtro=ones(size(E));
for i=1:width(E)
bu=find(E(:,i),1,'first');
filtro(1:bu,i)=0;
end
filtro
filtro = 5×3
0 0 0 0 0 0 1 0 1 1 1 1 1 1 1

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采纳的回答

Matt J
Matt J 2024-2-3
编辑：Matt J 2024-2-4
Ran in:
E=[0 5 6 9 2;0 0 1 3 1;0 5 4 2 4]';
[~,I]=max(logical(E),[],1);
filtro=(1:height(E))'>I
filtro = 5×3 logical array
0 0 0 0 0 0 1 0 1 1 1 1 1 1 1

更多回答（1 个）

Catalytic
Catalytic 2024-2-4
Ran in:
I don't know if "velocize" (not a word) is supposed to mean "accelerate" or "vectorize". The two are not the same.
If you're looking for the fastest possible code, there's no way to know in advance because it depends on the sparsity of E. For very dense E, your loop will probably be faster than @Matt J's answer.
E=rand(5000,3000)>0.1;
tic
filtro=true(size(E));
for i=1:width(E)
bu=find(E(:,i),1,'first');
filtro(1:bu,i)=0;
end
toc
Elapsed time is 0.016652 seconds.
tic
[~,I]=max(logical(E),[],1);
filtro=(1:height(E))'>I;
toc
Elapsed time is 0.031441 seconds.
  1 个评论
Matt J
Matt J 2024-2-4
Ran in:
True, but be mindful of the flipside:
E=rand(5000,3000)>0.7;
tic
filtro=true(size(E));
for i=1:width(E)
bu=find(E(:,i),1,'first');
filtro(1:bu,i)=0;
end
toc
Elapsed time is 0.051811 seconds.
tic
[~,I]=max(logical(E),[],1);
filtro=(1:height(E))'>I;
toc
Elapsed time is 0.020633 seconds.

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