Great.
Thank you for another swift reply.
Best,
Alex
________________________________________
From: graph-tool [[email protected]] on behalf of Tiago de Paula
Peixoto [[email protected]]
Sent: Wednesday, April 12, 2017 15:49
To: [email protected]
Subject: Re: [graph-tool] edge removal not removing value from property map
On 12.04.2017 14:12, Hobé Alex wrote:
> Hi Guys
>
> I am trying to remove edges from my graph.
>
> I first copy my graph:
> gCopy = g.copy()
> pCopy = gCopy.new_edge_property("double")
>
> then I go through the edges in the original graph to check for a particular
> property:
> for j, e in enumerate(g.edges():
> src = e.source()
> tgt = e.target()
>
> When a certain value for the property map of the original graph is found I
> use:
> if p[e] > value:
> print pCopy.a
> gCopy.remove_edge(e)
> print pCopy.a
(Side note: You should never remove vertices or edges during iteration,
since this can invalidate iterators. You should store them first, and delete
them after the loop.)
> When I look at pCopy.a I see that the array does not shorten and that 0
> values remain.
> These values do not show up when I use:
> for e in gCopy.edges():
> print pCopy[e]
>
> I can still find these values, however, when I use
> for e in g.edges():
> print pCopy[e]
This is totally normal. The property maps are simple C++ vectors which are
indexed by the edge index. As is explained in the documentation, when an
edge is removed, the indices of the remaining ones are not modified. This is
done for efficiency reasons.
> I want to use this array in the max flow algorithm and it complains:
> res = gt.edmonds_karp_max_flow(gCopy, src, tgt, pCopy)
> res.a = pCopy.a - res.a
> ValueError: operands could not be broadcast together with shapes (17,) (32,)
>
> Is there any way I can remove the zero values from pCopy.a?
Just use res.fa instead of res.a.
The .fa attribute returns a filtered array to the actual edges, whereas .a
always returns the naked underlying array.
Best,
Tiago
--
Tiago de Paula Peixoto <[email protected]>
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