On Wed, May 22, 2013 at 6:28 AM, Marie Lalanne <[email protected]> wrote:
> Hi Gabor,
>
> many thanks for your quick answer.
>
> When I write one of the command with "g[a,b]", R is telling me that the
> dimension is not correct. I guess this is due to the graph object (which is
> a list of edges so R understands one dimension, maybe?)
>
Maybe you have an old igraph version, or get this is weird bug with the
most recent version. It does not work for the first call, but it does for
the second and others. If you explicitly load the Matrix package, then it
is all good:
library(Matrix)
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
sum(colSums(g[s,-s]) != 0)
The command "shortest.paths" cannot have as argument "to=1" so I have found
> the following way to compute the shortest path:
>
Maybe you really have an old igraph version. The most recent version does
have a 'to' argument:
http://igraph.sourceforge.net/doc/R/shortest.paths.html
> c<-get.all.shortest.paths(g, v, to=s)
> d<-lapply(c, length)
> min(unlist(d))
>
> I did a mistake in my first question: in my example, the number of
> vertices connected to s would be 3 but I would like to get the number 2
> instead (because I want to count 1 for the link 2-5 and 1 for the links 1-3
> and 2-3).
>
I think my code does give 2.
Gabor
>
> Many thanks again for all your help!
> Very best,
> Marie
>
>
>
> ------------------------------
> *De :* Gábor Csárdi <[email protected]>
> *À :* Marie Lalanne <[email protected]>; Help for igraph users <
> [email protected]>
> *Envoyé le :* Mardi 21 mai 2013 18h57
> *Objet :* Re: [igraph] degrees of separation
>
> 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
>
>
>
--
Gabor Csardi <[email protected]> MTA KFKI RMKI
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