How to quickly find the first non-zero element without iterations in all columns in a sparse matrix?
90 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hi, All,
I have a big sparse matrix A. I want to find out the first non-zero element in all columns from the top. Here is my code:
reorderCol = [];
for jCol = 1 : length(A(1,:))
eee = find(A(:,jCol),1,'first');
reorderCol = [reorderCol eee];
end
For example, I have matrix A = [0 0 0;0 5 0;0 0 1;0 0 0;-1 0 -4]. My code gives the following result:
reorderCol = [5 2 3];
I am wondering if it is possible to obtain reorderCol without iterations. Thanks a lot.
Benson
0 commentaires
Réponse acceptée
Plus de réponses (3)
Les Beckham
le 18 Mar 2020
Modifié(e) : Les Beckham
le 18 Mar 2020
Try this. In my test with a 1000x1000 random sparse 0 or 1 matrix (A = sparse(randi([0 1], 1000, 1000));) it is about 4 times faster.
i = find(A(:) ~= 0, 1, 'first');
ij = ind2sub(size(A), i);
For a 5000x5000 A it is actually slower, however (about 83% as fast).
Note that I am using Octave as I don't currently have access to Matlab.
Iteration is not always necessary, or desirable, to avoid. In fact, many of the Matlab 'tricks' are just iteration in disguise.
I hope this helps.
Perhaps your results will be different using Matlab vs. Octave. Let me know.
Voir également
Catégories
En savoir plus sur Genomics and Next Generation Sequencing dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!