[R] vertex labels in igraph from adjacency matrix

[Charilaos Skiadas]

On Mar 5, 2008, at 1:39 AM, Mark W Kimpel wrote:

> I am getting some unexpected results from some functions of igraph and
> it is possible that I am misinterpreting the vertex numbers. Eg., the
> max betweenness measure seems to be from a vertex that is not  
> connected
> to a single other vertex. Below if my code snippet:
>
> require(igraph)
> my.graph <- graph.adjacency(adjmatrix = my.adj.matrix, mode=c 
> ("undirected"))
>
> most.between.vert <- colnames(my.adj.matrix)[which(betweenness(graph =
> my.graph, v=V(my.graph), directed = FALSE) == max(betweenness(graph =
> my.graph, v=V(my.graph), directed = FALSE))) + 1]

What is the +1 for? Seems to me that this would give you the wrong  
vertex, since you find the vertex which is the max, and then you ask  
it to give you the next vertex in the list.

Btw, you will likely want to take the betweenness call out, and call  
it once and store the result, instead of calling it twice (well,  
assuming the graph is largish). Or even better, use which.max:

which.max(betweenness(graph = my.graph, v=V(my.graph), directed =  
FALSE))

Haris Skiadas
Department of Mathematics and Computer Science
Hanover College

> sum(my.adj.matrix[most.between.vertext,])
> 0
>
>
> Is there a way to automatically set the vertex name attributes from  
> the
> row and colnames of the inputted adjacency matrix to graph.adjacency?
> This would seem like an intuitive feature, but I can't find it
> documented. In the absence of this feature, how can I make sure that I
> am setting the vertex name attributes correctly?
> -- 
>
> Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
> Indiana University School of Medicine
>
> 15032 Hunter Court, Westfield, IN  46074
>
> (317) 490-5129 Work, & Mobile & VoiceMail
> (317) 204-4202 Home (no voice mail please)
>
> mwkimpel<at>gmail<dot>com
>