How to find the last 1 in every row

4 vues (au cours des 30 derniers jours)
Alex
Alex le 26 Nov 2020
Modifié(e) : Bruno Luong le 26 Nov 2020
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;

Réponses (2)

KALYAN ACHARJYA
KALYAN ACHARJYA le 26 Nov 2020
Modifié(e) : KALYAN ACHARJYA le 26 Nov 2020
A=rot90(A,90);
[~,idx]=max(A==1,[],2)
Result:
idx =
2
3
2

Bruno Luong
Bruno Luong le 26 Nov 2020
Modifié(e) : Bruno Luong le 26 Nov 2020
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

Catégories

En savoir plus sur Logical dans Help Center et File Exchange

Produits

Community Treasure Hunt

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

Start Hunting!

Translated by