Construct adjacency list from an adjacency matrix

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Saurabh
Saurabh 2014-3-4
评论： Alec Jacobson 2021-5-17
I have an adjacency matrix :-
E.g A =[0 1 1;1 0 0; 1 0 0];
output :
2 3
1
1
I want to create an adjacency list from this matrix.

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回答（1 个）

Azzi Abdelmalek
Azzi Abdelmalek 2014-3-4
A =[0 1 1;1 0 0; 1 0 0]
B=cellfun(@(x) find(x),num2cell(A,2),'un',0)
celldisp(B)
  1 个评论
Alec Jacobson
Alec Jacobson 2021-5-17
This will be very slow for large graphs even if your adjacency matrix A is sparse: num2cell effectively creates a dense matrix.
As a drop-in replacement you could use:
B = arrayfun(@(i) find(A(:,i))',1:size(A,2),'UniformOutput',false)';
However, depending on how you're using this adjacency list it might be better to just use find(A(:,i) any time you need i's neighbors: the compressed column storage of matlab's sparse matrices is tantamount to storing an adjacency list anyway.

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