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## Re: [igraph] count neighbourhood (python)

**From**: |
Raphael Clifford |

**Subject**: |
Re: [igraph] count neighbourhood (python) |

**Date**: |
Sat, 15 Sep 2012 10:09:14 +0100 |

I tested the running time of the igraph implementation of
neighborhood_size it does indeed appear to be fast and memory
efficient (although I don't know exactly how it works). I would also
like to count the number of edges within a 2 hop neighborhood of each
node. One way is
[g2.subgraph(g2.neighborhood(v, order = 2)).ecount() for v in g.vs]
Is there a better/faster igraph way?
Raphael
On 15 September 2012 09:21, Raphael Clifford <address@hidden> wrote:
>* I would like to count the number of vertices within a 2 hop distance*
>* of each node in a large sparse graph. I see there is a function which*
>* one could call with neighborhood size(vertices=g.vs, order=2). What*
>* method is used to do the calculation?*
>
>* A classic way to do it would be to represent the graph as a sparse*
>* matrix, square it using a clever sparse matrix multiplication*
>* algorithm and count the number of elements in each row that are*
>* non-negative. I am wondering how this would compare to the*
>* implemented method in igraph. Can igraph make a sparse matrix that*
>* could be fed directly into*
>* http://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.csr_matrix.html#scipy.sparse.csr_matrix*
>* for example?*
>
>* Raphael*