Use this if you are using igraph from R
Union of vertex sequences
## S3 method for class 'igraph.vs' union(...)
The vertex sequences to take the union of.
They must belong to the same graph. Note that this function has
‘set’ semantics and the multiplicity of vertices is lost in the
result. (This is to match the behavior of the based
A vertex sequence that contains all vertices in the given sequences, exactly once.
Other vertex and edge sequence operations:
g <- make_(ring(10), with_vertex_(name = LETTERS[1:10])) union(V(g)[1:6], V(g)[5:10])