CODEWITHSUNDEEP
matlabsparse-matrixmatrix-indexing
Lisa
Lisa

Reputation: 3526

MATLAB accessing multiple elements in sparse matrix using row and column index vectors

I feel there should be an easy solution but I can't find it:

I have the sparse matrices A B with the same dimension n*n. I want to create matrix C which copies values in A where B is non-zero.

This is my approach:

[r,c,v] = find(B);

% now I'd like to create an array of values using indices r and c, 
% but this doesn't work (wrong syntax)
v2 = A(r,c);

% This won't work either
idx = find(B); % linear indexing, too high-dimensional
v2 = A(idx);

% and create C
C = sparse(r,c,v2,n,n);

Here are some more details:

Is there really no way to use 2-dimensional indices?

Thanks for your help!

Upvotes: 4

Views: 1426

Answers (1)

Da Kuang
Da Kuang

Reputation: 892

I think C = A .* (B~=0); should work. Only non-zeros will be accessed in the entrywise multiplication of two sparse matrices so it will be fast.

Upvotes: 4

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