How to find the last 1 in every row

Question

Alex 2020-11-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/663478-how-to-find-the-last-1-in-every-row

编辑： Bruno Luong 2020-11-26

Simliar to this question, but for finding the last 1 in each row.

Say I have a matrix

A = [0 1 1 1 0;
     1 1 1 0 0;
     0 1 1 1 0]

What's the fastest way to find the last 1 in each row? The output should be

ans = [2; 3; 2];

So far I have come up with this:

[~, I] = max(fliplr(A),[],2);
I = size(A,2) + 1  - I;

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

KALYAN ACHARJYA 2020-11-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/663478-how-to-find-the-last-1-in-every-row#answer_556968

编辑：KALYAN ACHARJYA 2020-11-26

在 MATLAB Online 中打开

A=rot90(A,90);
[~,idx]=max(A==1,[],2)

Result:

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Bruno Luong 2020-11-26

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/663478-how-to-find-the-last-1-in-every-row#answer_556983

编辑：Bruno Luong 2020-11-26

在 MATLAB Online 中打开

Depending on the density of 1s, but a for-loop (remember that?) might be the fatest

function BenchMax
A=rand(10000)>0.5;
tic
[~, I] = max(fliplr(A),[],2);
I = size(A,2) + 1  - I;
toc % Elapsed time is 0.045622 seconds.
tic
[m,n] = size(A);
I = zeros(m,1);
for r=1:m
    for c=n:-1:1
        if A(r,c)
            I(r) = c;
            break
        end
    end
end
I = n+1-I;
toc % Elapsed time is 0.000437 seconds.
end