Hi, please see below.
On Tue, May 21, 2013 at 12:11 PM, Marie Lalanne <[email protected]> wrote:
> Hello,
>
> I am a new R and igraph user and I am wondering whether you could give me
> some hints to do the following:
>
Assuming 'g' is the graph, 's' the subset and 'v' the vertex:
library(igraph)
data <- "1 2
1 3
2 3
2 5
3 4
3 5
4 5
"
g <- graph.data.frame(read.table(textConnection(data)),
directed=FALSE, vertices=data.frame(1:5))
s <- c(1,2)
v <- 4
> I have an edgelist (undirected). I would like to compute the following
> four things:
> - for a subset of vertices, the number of edges (without counting twice a
> same vertex linked with two different vertices of the subset)
>
So this is effectively the number of vertices connected to s?
sum(colSums(g[s,-s]) != 0)
> - for a subset of vertices, if at least one of the vertices from this
> subset is linked with a particular vertex (from the whole set)
>
any(g[s,v] != 0)
> - for a subset of vertices, the minimal degree of separation required to
> reach a particular vertex (from the whole set)
>
min(shortest.paths(g, v=4, to=s))
> - for all the vertices (in the whole set), if they are linked with at
> least one vertex from the subset
>
colSums(g[s,]) != 0
Please see the manual, in particular ?'[.igraph' for details.
Best,
Gabor
ps. be critical with my answers, and check them, I haven't checked them too
extensively.
> For example:
> 1-2
> 1-3
> 2-3
> 2-5
> 3-4
> 3-5
> 4-5
> and consider the subset of vertices being 1 and 2 and the particular
> vertex being 4
> Answer to the first question: 3 (edges 1-3 and 2-3 are count only for one)
> Answer to the second question: 0 (neither 1, neither 2 is directly linked
> to 4)
> Answer to the third question: 2 (edge 1-3 and then edge 3-4 or edge 2-3
> and then edge 3-4)
> Answer to the fourth question: [1] - [2] - [3] 1 [4] 0 [5] 1
>
> Many thanks for your help!
>
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>
>
--
Gabor Csardi <[email protected]> MTA KFKI RMKI
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