help finding edge connecting two nodes

Hello,

You should give a reproducible example showing us what you have tried, 
with an example dataset.
Try the following.

# A graph I've just drawn
v <- c(1,2,1,3,1,4,2,5,2,4,3,5,3,6,5,7,5,8,5,10,6,8,6,10,7,8,7,9,8,9)
g <- graph(v, directed = FALSE)
plot(g, layout=layout.fruchterman.reingold)
E(g)$weight <- 1:15

# This is what you want
E(g)[5 %--% 10]$weight


See the help for

?igraph::iterators


Hope this helps,

Rui Barradas
Em 18-10-2012 23:05, dhaval at mit.edu escreveu:

I'm new to R and igraph and I was wondering if anybody can help me with the
following.

I want to find the edge weight between two vertices in a graph. My graph
structure is defined by the normal ego (node1), alter (node2) and the weight
of the edge between them.

I know that I can get the weight for each of the edges in the list of edges
that originate from node number 5 using E(igraph_friendship) [ from(5)
]$weight And that I can find the weight for each of the edges in the list of
edges that end onto node number 10 using E(igraph_friendship) [ to(10)
]$weight

But what if I simply want to find the weight of the edge that simple
connects just node 5 and node 10?

Alternatively, if I can get the identifier of the edge that connects node 5
and 10 in the list of all edges, E(igraph_friendship), that would work too.

Thanks a lot for your help, I've been looking around a lot for it and I
really appreciate your help!



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[...]

Your way works best! Another way I found from stackoverflow (see the post
at
http://stackoverflow.com/questions/12964332/igraph-edge-between-two-vertices/12980550#12980550)
was
to convert the graph into an adjacency matrix and then use simple matrix
indices .

Just make this clear. The example (repeated below) on the
stackoverflow page does _not_ convert the graph into an adjacency
matrix. The indexing only makes the graph look as if it was an
adjacency matrix. But there is no conversion at all.

Gabor

ps. I would appreciate if you didn't cross-post your questions
everywhere (R-help, igraph-help and stackoverflow, maybe other places
as well). Please only post it on the platform you prefer first and
then, if you don't get a good answer, try elsewhere. Thanks!

library(igraph)
g <- graph.ring(10)
g[1,2]
# [1] 1
E(g)$weight <- runif(ecount(g))
g[1,2]
# [1] 0.8115639

[...]