Relation of Elements of matrix
4 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
ANAND ASP
le 29 Jan 2021
Commenté : Walter Roberson
le 29 Jan 2021
A = [1 2
2 6
2 3
2 7
3 4
5 4
6 3
4 7]
i have matrix A,
if i select B=2, i want output as 1 2 3 6 7, it shows relatiionship of 2
if i select B=3, i want output as 2 3 4 6, it shows relatiionship of 3
1 commentaire
Réponse acceptée
Walter Roberson
le 29 Jan 2021
Modifié(e) : Walter Roberson
le 29 Jan 2021
A = [1 2
2 6
2 3
2 7
3 4
5 4
6 3
4 7]
B = 2
unique([B; A(A(:,1) == B,2); A(A(:,2) == B,1)]).'
However, the basis for including the number itself is not clear. If B does not occur at all in A, then I would argue it would be more appropriate for the result to be empty than for it to include B itself.
6 commentaires
Paul Hoffrichter
le 29 Jan 2021
Modifié(e) : Paul Hoffrichter
le 29 Jan 2021
After adding a note that removing the sort was faster, I then started thinking that the two line solution might actually be faster than the more one-line solution. (Usually, I think of one-line solutions as not only more elegant, but also, usually also faster.)
Yet, the two line solution was 4-5 times faster than the one line solution. Not that it matters much since the time for either one is negligible.
B = 12345;
n = 1e8;
A = randi(n/2000,n,2);
tic
z1 = unique([B; A(A(:,1) == B,2); A(A(:,2) == B,1)]).';
toc
tic
[r, ~] = ind2sub( size(A), find(A==B) );
z2 = unique( A( r ,: ) )';
toc
Elapsed time is 0.665452 seconds.
Elapsed time is 0.154779 seconds.
Walter Roberson
le 29 Jan 2021
B = 12345;
n = 5e7;
A = randi(n/2000,n,2);
tic
z1 = unique([B; A(A(:,1) == B,2); A(A(:,2) == B,1)]).';
toc
tic
[r, ~] = ind2sub( size(A), find(A==B) );
z2 = unique( A( r ,: ) )';
toc
tic
z3 = unique(A(any(A == B,2),:)).';
toc
Plus de réponses (1)
Paul Hoffrichter
le 29 Jan 2021
B = 3;
[r, ~] = ind2sub( size(A), find(A==B) );
z = A(sort(r),:);
zu = unique(z(:))'
2 commentaires
Paul Hoffrichter
le 29 Jan 2021
B = 2;
[r, ~] = ind2sub( size(A), find(A==B) );
z = unique( A( sort(r) ,: ) )'
Paul Hoffrichter
le 29 Jan 2021
Don't need the sort, so this is faster:
[r, ~] = ind2sub( size(A), find(A==B) );
z = unique( A( r ,: ) )'
Voir également
Catégories
En savoir plus sur Logical 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!