CODEWITHSUNDEEP
matlaboctave
user3635284
user3635284

Reputation: 513

How to dump non-zero elements of a sparse matrix into a non-sparse matrix

I could have also asked how to dump a sparse matrix to CSV basically I have a graph represented as a sparse matrix and I want to export the graph to CSV to open it in Gephi. So my sparse matrix is something like:

(23,35) 1

(35,78) 1

(78,23) 1

etc

I would like to convert this into a vector like: [23,35,1;35,78,1;78,23,1]

I would love to know there's a simple one-liner to do it but I can't make my brain find it so thanks a lot for the help.

If you alternatively known something as sparse2csv('graph.csv',Adj) that would generate in a file:

23,35,1

35,78,1

78,23,1

Then that would work too.

Upvotes: 1

Views: 86

Answers (1)

TroyHaskin
TroyHaskin

Reputation: 8401

The way that comes to mind isn't a one-liner (though it could easily be made one via a function) but simply uses two function calls: find and nonzeros:

A       = sparse([23;35;78],[35;78;23],[1;1;1]);
[r,c]   = find(A~=0);
v       = nonzeros(A);
compact = [r,c,v];
disp(compact);

which returns

78    23     1
23    35     1
35    78     1

As Luis Mendo points out in the comments, a simpler solution exists since find will return the nonzero values in a third output argument (the given array is no longer logical either now):

[r,c,v] = find(A);
compact = [r,c,v];

Upvotes: 3

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