Construct adjacency list from an adjacency matrix

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.

Answer 1

[Azzi Abdelmalek]

A =[0 1 1;1 0 0; 1 0 0]
B=cellfun(@(x) find(x),num2cell(A,2),'un',0)
celldisp(B)

[Alec Jacobson]

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.