Re: [igraph] Methods for getting disconnected pairs and for common neighbors

[Tamas Nepusz]

Hi,

Just answered this on Stack Overflow but here it is again so people can find
the answer on the mailing list as well:

Re the first question (listing pairs of disconnected nodes): yes, you have to
do this manually, but it is fairly easy:

from itertools import product
            
all_nodes = set(range(g.vcount())
disconnected_pairs = [list(product(cluster,all_nodes.difference(cluster))) \
                      for cluster in g.clusters()]

But beware, this could be a fairly large list if your graph is large and
consists of a lot of disconnected components.

Re the second question (listing common neighbors): again, you have to do this
manually but it only takes a single set intersection operation in Python:

set(g.neighbors(v1)).intersection(set(g.neighbors(v2)))

If you find that you need to do this for many pairs of nodes, you should
probably create the neighbor sets first:

neighbor_sets = [set(neis) for neis in g.get_adjlist()]

Then you can simply write `neighbor_sets[i]` instead of `set(g.neighbors(i))`.

T.

On 11/24, Merton Lister wrote:
> Hi everyone,
> 
> I have two questions about methods available in the igraph python package.
> 
> Is there a method that would return all the unconnected pairs of nodes in
> an undirected graph? Ideally, there is no duplicate as (1, 2) and (2, 1)
> are the same in this context.
> 
> In addition, given two nodes in an undirected graph, is there a method that
> returns their common neighbors?
> 
> Many thanks for your help!
> 
> Best regards,
> Merton

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-- 
T.