Id's, once again

Hi all, I am new here. I looked into the mail archive but I did not get
what I was looking for despite old subjects about id's.

I have extracted the strongly connected component (scc) from a graph that I
built from a transportation network. I want to identify the nodes of the
network that are not connected to the scc. I am able to get the index of
the vertices in the graph but I did not find an obvious way to get the id's
of these vertices to extract them from my original network.


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I think that one solution may be to use a graphview or a filter: you should
filter out the nodes that belong to the scc, then you can iterate over the
remaining vertices and retrieve any property they have.


2014-05-23 21:56 GMT+02:00 Flavien Lambert <petit.lepton(a)>:

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Hi! Thanks for the answer! I managed to retrieve the nodes easily but my
main concern is to get the property id in fact...

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I don't fully understand what the difficulty is. Could you perhaps be
more specific, preferably with a short example?


Hi, I am sorry, I think there is no difficulty. It is just that I did not
get how to get the id once you have the node index :

from graph_tool.all import *

So from u, I get the indices (for the 0 entries). I would like to know what
are the id's of the graph_tool vertices in my original nodeNetwork.graphml.

Thanks for the great work by the way!

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That depends on what you mean by "id". Each vertex in the graph has an
associated index, which is retrieved via the vertex_index attribute of
the graph:

    idx = g.vertex_index[v]

or equivalently

    idx = int(v)

However, if you are referring to some property map stored in your
graphml file which you call "id", then this resides inside the internal
property maps of the graph:

    id_map = g.vp["id"]
    id = id_map[v]

And finally, if you want the intrinsic ids inside the graphml file if
they are not in canonical form, this can be retrieved via:

    id_map = g.vp["_graphml_vertex_id"]
    id = id_map[v]


That is perfect! Thanks a lot!

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