Use this if you are using igraph from R
Concatenate vertex sequences
## S3 method for class 'igraph.vs' c(..., recursive = FALSE)
| ... | The vertex sequences to concatenate. They must refer to the same graph. | 
| recursive | Ignored, included for S3 compatibility with
the base  | 
A vertex sequence, the input sequences concatenated.
Other vertex and edge sequence operations: c.igraph.es,
difference.igraph.es,
difference.igraph.vs,
igraph-es-indexing2,
igraph-es-indexing,
igraph-vs-indexing2,
igraph-vs-indexing,
intersection.igraph.es,
intersection.igraph.vs,
rev.igraph.es, rev.igraph.vs,
union.igraph.es,
union.igraph.vs,
unique.igraph.es,
unique.igraph.vs
g <- make_(ring(10), with_vertex_(name = LETTERS[1:10])) c(V(g)[1], V(g)['A'], V(g)[1:4])