Thanks Tiago!
Let me just point out that the part
mask.a = g.degree_property_map("out").a > 4
will (if you are using python 2.x) not give you what you most likely would
like to have, namely a list of boolean values containing the results of the
element wise comparisons of elements g.degree_property_map("out").a[i]>4.
Instead, for some strange reason, you'll simply get the *value* True back,
writing True to all elements in mask.a ... instead, it seems to me, the
only (fastest) way to do it is to use map
mask.a = map(lambda(x): x > 4, g.degree_property_map("out").a)
.... so be careful.
Cheers,
René
On 30 September 2013 16:13, Tiago de Paula Peixoto <[email protected]> wrote:
> Hi René,
>
> On 09/30/2013 03:57 PM, Rene Pfitzner wrote:
> > Hi everyone,
> >
> > this might be easily solved, but anyways:
> >
> > I have been thinking whether there is a fast way of retrieving
> > property map values of subsets of nodes? I mean the following: let's
> > say I have a property map A, defined for all vertices of graph G. Now,
> > lets say I have a vertex iterator V that spans a subset of all nodes
> > of G. Is there now a fast way, to a) read and b) eventually change the
> > values in A of all nodes in V, e.g. to do something like A[V] and to
> > get an array back, like in A.a ....
> >
> > Of course, iterating or map would be obvious options, but take
> > eventually a lot of time. Another idea I had was, let's say the
> > property map is an internal property map, to use vertex_filter and
> > then get A.a. But what if the property map is not internal?
>
> This is easily done with graph filters, as you suggest. It does not
> matter whether or not the property maps are internal.
>
> For instance, suppose you want to modify the property of all nodes with
> a degree larger than four. You could do:
>
> g = ... # this is your graph
> prop = ... # this is your property
>
> mask = g.new_vertex_property("bool")
> mask.a = g.degree_property_map("out").a > 4
> g.set_vertex_filter(mask)
>
> prop.fa = 42 # this only affects the filtered values
>
> You can also do it using a graph view:
>
> u = GraphView(g, vfilt=g.degree_property_map("out").a > 4)
> uprop = u.own_property(prop)
> uprop.fa = 42
>
> I prefer the last one, since it is more compact.
>
> (Note the use of A.fa instead of A.a)
>
> Cheers,
> Tiago
>
>
> --
> Tiago de Paula Peixoto <[email protected]>
>
>
--
René Pfitzner, Dipl. Phys.
Scientific assistant / Doctoral candidate
ETH Zürich
Chair of Systems Design
+41-44-63-28478
[email protected]
http://www.sg.ethz.ch/people/prene
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