Re: [igraph] key players in networks

[Simone Gabbriellini]

Gabor,

sorry for the delay in answering you, and thanks a lot for your help!

I'll try this code in the next days with my networks and let you know.

thank you again,

all the best,
Simone


Il giorno 13/set/07, alle ore 16:26, Gabor Csardi ha scritto:

> Ok, I read the paper, the measures are not very difficult,
> although optimizing them is a different question.
> Here is how to calculate DF and DR:
>
> df <- function(g) {
>   n <- vcount(g)
>   spmat <- shortest.paths(g)
>   spmat[spmat==n] <- Inf
>   dists <- spmat[upper.tri(spmat)]
>   1-2*sum(1/dists)/n/(n-1)
> }
>
> dr <- function(g, k) {
>   n <- vcount(g)
>   spmat <- shortest.paths(g, k)
>   dkj <- apply(spmat, 2, min)
>   dkj <- dkj[ dkj != 0 ]
>   dkj[dkj==n] <- Inf
>   sum(1/dkj)/n
> }
>
> df works well for the two toy graphs:
>
> g1 <- graph.full(5) %du% graph.full(5)
> g2 <- graph.ring(5, circ=FALSE) %du% graph.ring(5, circ=FALSE)
>
> I couldn't try them for the two real networks in the paper, because
> i couldn't find the data, for the second one even the cited reference
> is missing from the bibliography.
>
> Now you can try to make up some optimization function using
> 'delete.vertices' from igraph and the 'df' and 'dr' functions
> defined as above. If k is small (2-4) then you can brute force
> all cases, for larger k and larger networks a more sophisticated
> algorithm might be needed. Unfortunately i don't know any R
> functions doing 'subgraph optimization' like this.
>
> Best,
> Gabor
>
> On Thu, Sep 13, 2007 at 10:55:59AM +0200, Gabor Csardi wrote:
> > Simone,
> >
> > hmmm, igraph has many functions for centrality, some simple ones like
> > degree and closeness and some more sophisticated like page rank and
> > Burt's constraints.
> >
> > The new measures in the mentioned paper are not included yet.
> > I'll include them if the interest/work ratio is above my threshold,
> > thanks for the reference.
> >
> > But be aware that these measures work for you only if you're
> > interested in exactly the same functional roles they were developed
> > for. Ie. if you're interested in the vertices you'll end up most of
> > the time by randomly walking on the network then page rank is better,
> > etc. (if my (mis)conceptions about page rank are right).
> >
> > Gabor
> >
> > On Tue, Sep 11, 2007 at 01:57:58PM +0200, Simone Gabbriellini wrote:
> > > Hi all,
> > >
> > > I need to identify key players in my networks..
> > > I found some procedures by Borgatti, described in the article
> > > "Identifying sets of key players in a social network"..
> > >
> > > does igraph already has a function to find key players in networks?
> > >
> > > regards,
> > > Simone
> > >
> > >
> > > _______________________________________________
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> >
> > --
> > Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK
> >
> >
> > _______________________________________________
> > igraph-help mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/igraph-help
>
> --
> Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK
>
>
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