how to velocize it (avoid loop is possible)

1 次查看（过去 30 天）
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

请先登录，再回答此问题。

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.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by