If only one positive elem per row (rest are 0), then fill both sides of positive element
1 vue (au cours des 30 derniers jours)
Afficher commentaires plus anciens
Hi, I have a square matrix of non-negative elements. In each row, at least one element is positive.
For rows where there is only one positive element (the rest are 0) I need to put 1e-4 next to that element, both sides. In A below, the second and last row have only 1 positive (note last row has only one side to add)
A=...
[0.9 0.1 0 0;
0 0.8 0 0;
0 0.1 0.7 0.1;
0 0 0 0.9]
Ouput should be:
B=...
[0.9 0.1 0 0;
1E-4 0.8 1E-4 0;
0 0.1 0.7 0.1;
0 0 1E-4 0.9]
The dimension of the matrix is fixed, so I can get rows that need to be changed (if result is 3 in this case) with
sum(A==0,2)
But this doesn't tell me the position of the positive element (I could use something like find(A) ) , nor fill both sides (loop free if possible)
0 commentaires
Réponse acceptée
Guillaume
le 20 Fév 2015
A = [0.9 0.1 0 0
0 0.8 0 0
0 0.1 0.7 0.1
0 0 0 0.9];
Apadded = [zeros(size(A, 1), 1) A zeros(size(A, 1), 1)]; %pad to avoid dealing with edges
lonelyrows = find(sum(A ~= 0, 2) == 1);
[~, singlecols] = find(Apadded(lonelyrows, :));
Apadded(sub2ind(size(Apadded), [lonelyrows lonelyrows], [singlecols-1 singlecols+1])) = 1e-4;
Afilled = Apadded(:, 2:end-1)
0 commentaires
Plus de réponses (2)
Sean de Wolski
le 20 Fév 2015
Modifié(e) : Sean de Wolski
le 20 Fév 2015
And just for fun:
A=...
[0.9 0.1 0 0;
0 0.8 0 0;
0 0.1 0.7 0.1;
0 0 0 0.9];
B = A;
sgn = sign(A)==1;
B(logical(conv2(double(bsxfun(@and,sum(sgn,2)==1,sgn)),[1 0 1],'same'))) = 1e-4
1 commentaire
dpb
le 20 Fév 2015
Find the locations needing to be worked around. Pick one dimension first as you've done; I'll stick with the rows...
>> irow=find(sum(A>0,2)==1)
irow =
2
4
>> [~,icol]=ind2sub(size(A(irow,:)),find(A(irow,:)>0))
icol =
2
4
>>
These are now indices in the original array since didn't reduce the number of columns by subselecting the rows.
2 commentaires
dpb
le 20 Fév 2015
Ran out of time...methinks bsxfun the irow,icol array of indices with padded array as Guillame did would also work...
Voir également
Catégories
En savoir plus sur Startup and Shutdown 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!