Bed of Nails from vectors - inverse of find()?
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Douglas Anderson
el 27 de Feb. de 2018
Comentada: Jos (10584)
el 28 de Feb. de 2018
Hello,
I would like to do the following:
X = zeros(N,M); % Say N = 50, M = 100
Then have N sets of indices, one for each row of X:
a(1,:) = [ 1 5 10 12 19 32 56 ...]; % These may vary substantially
a(2,:) = [ 1 7 14 19 29 45 76 ...];
...
These are then indices that will indicate where there should be a "1" in each row of X.
Is there a function that will take the indices and then put a "1" in an array? This is kind of like the inverse of find().
Thanks!
Doug Anderson
2 comentarios
Jos (10584)
el 27 de Feb. de 2018
As your variable a is a N-by-K matrix, this assumes that all rows of X will hold K ones. Is that so?
Respuesta aceptada
Jos (10584)
el 27 de Feb. de 2018
% input
N = 5 ; M = 4 ;
a = [1 3 ; 2 4 ; 1 4 ; 1 2 ; 3 4]
% engine in one line
XX = full(sparse(repmat(1:N, size(a,2), 1)', a, 1,N,M))
2 comentarios
Jos (10584)
el 28 de Feb. de 2018
This might not be the most efficient way though.
See the documentation of sparse for more details.
Más respuestas (2)
Jos (10584)
el 27 de Feb. de 2018
N = 5 ; M = 4 ;
a = [1 3 ; 2 4 ; 1 4 ; 1 2 ; 3 4]
X = zeros(N,M)
X(sub2ind([N M], repmat(1:N, size(a,2), 1)', a)) = 1
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