VertexIndex

VertexIndex[g,v] gives the integer index for the vertex v in the graph g.

VertexIndex[{v->w,…},…] uses rules v->w to specify the graph g.

Examples

Get the index of a vertex:

g = Graph[{a -> b, b -> c, c -> a}];
VertexIndex[g, b]
(* 2 *)

Using edge rules directly:

VertexIndex[{1 -> 2, 2 -> 3}, 3]
(* 3 *)

Please visit the official Wolfram Language Reference for more details.