How do I find the edges of a vertex using igraph and R?

Question

Say I have this example graph, i want to find the edges connected to vertex 'a'

 d <- data.frame(p1=c('a', 'a', 'a', 'b', 'b', 'b', 'c', 'c', 'd'),                  p2=c('b', 'c', 'd', 'c', 'd', 'e', 'd', 'e', 'e'))  library(igraph) g <- graph.data.frame(d, directed=FALSE) print(g, e=TRUE, v=TRUE) 

I can easily find a vertex:

 V(g)[V(g)$name == 'a' ] 

But i need to reference all the edges connected to the vertex 'a'.

Answer 1

See the documentation on igraph iterators; in particular the from() and to() functions.

In your example, "a" is V(g)[0], so to find all edges connected to "a":

E(g) [ from(0) ] 

Result:

[0] b -- a [1] c -- a [2] d -- a 

Answer 2

If you do not know the index of the vertex, you can find it using match() before using the from() function.

idx <- match("a", V(g)$name) E(g) [ from(idx) ]